Optical discs for Facebook cold storage

I heard last week that Facebook is implementing Blu Ray libraries for cold storage. Each BluRay disk holds ~100GB and they figure they can store 10,000 discs or ~1PB in a rack.

They bundle 12 discs in a cartridge and 36 cartridges in a magazine, placing 24 magazines in a cabinet, with BluRay drives and a robotic arm. The robot arm sits in the middle of the cabinet with the magazines/cartridges located on each side.

It’s unclear what Amazon Glacier uses for its storage but a retrieval time of 3-5 hours indicates removable media of some type.  I haven’t seen anything on Windows Azure offering a similar service but Google has released Durable Reduced Availability (DRA) storage which could potentially be hosted on removable media as well.  I was unable to find any access times specifications for Google DRA.

Why the interest in cold storage?

The article mentioned that Facebook is testing the new technology first on its compliance data. After that Facebook will start using it for cold photo storage. Facebook also said that it will be using different storage technologies for it’s cold storage repository mentioning “bad flash” as another alternative.

BluRay supports both a re-writeable as well as WORM (write once, read many times) technology. As such, WORM discs cannot be modified, only destroyed.  WORM technology would be very useful for anyone’s compliance data. The rewritable Blu Ray discs might be more effective for cold photo storage, however the fact that people on Facebook rarely delete photos, says WORM would work well here too.

100GB is a pretty small storage bucket these days but for compliance documents, such as email, invoices, contracts, etc. it’s plenty large.

Can Blu Ray optical provide data center cold storage?

Facebook didn’t discuss the specs on the robot arm that they were planning to use but with 10K cartridges it has a lot of work to do. Tape library robots move a single cartridge in about 11 seconds or so. If the optical robot could do as well (no information to the contrary) one robot arm could support ~4K disc moves per day. But that would be enterprise class robotics and 100% duty cycle, more likely 1/2 to 1/4 of this would be considered good for an off the shelf system like this. So maybe a 1000 to 2000 disc picks per day.

If we use 22 seconds per disc swap (two disc moves), a single robot/rack could support a maximum of 100 to 200TB of data writes per day (assuming robot speed was the only bottleneck).  In the video (see about 30 minutes in) the robot didn’t look all that fast as compared to a tape library robot, but maybe I am biased.

Near as I can tell a 12x BluRay drive can write at ~35MB/sec (SATA drive, writing single layer, 25GB disc, we assume this can be sustained for a 4-layer or dual-sided 2-layer 100GB disc). So to be able to write a full 100GB disk would take ~48 minutes and if you add to that the 22 seconds of disc swap time, one SATA drive running 100% flat out could maybe write 30 discs per day or ~3TB/day.

In the video, the BluRay drives appear to be located in an area above the disc magazines along each side. There appears to be two drives per column with 6 columns per side, so a maximum of 24 drives. With 24 drives, one rack could write about 72TB/day or 720 discs per day which would fit into our 22 seconds per swap.  At 72TB/day it’s going to take ~14 days to fill up a cabinet. I could be off on the drive count, they didn’t show the whole cabinet in the video, so it’s possible they have 12 columns per side, 48 drives per cabinet and 144TB/day.

All this assumes 100% duty cycle on the drives which is unreasonable for an enterprise class tape drive let alone a consumer class BluRay drive. This is also write speed, I assume that read speed is the same or better. Also, I didn’t see any servers in the cabinet and I assume that something has to be reading, writing and controlling the optical library. So these other servers need to be somewhere close by, but they could easily be located in a separate rack somewhere near to the library.

So it all makes some amount of sense from a system throughput perspective. Given what we know about the drive speed, cartridge capacity and robot capabilities, it’s certainly possible that the system could sustain the disc swaps and data transfer necessary to provide data center cold storage archive.

And the software

But there’s plenty of software that has to surround an optical library to make it useful. Somehow we would want to be able to identify a file as a candidate for cold storage then have it moved to some cold storage disc(s), cataloged, and then deleted from the non-cold storage repository.  Of course, we probably want 2 or more copies to be written, maybe these redundant copies should be written to different facilities or at least different cabinets.  The catalog to the cold storage repository is all important and needs to be available 24X7 so this needs to be redundant/protected, updated with extreme care, and from my perspective on some sort of high-speed storage to handle archives of 3EB.

What about OpenStack? Although there have been some rumblings by Oracle and others to provide tape support in OpenStack, nothing seems to be out yet. However, it’s not much of a stretch to see removable media support in OpenStack, if some large company were to put some effort into it.

Other cold storage alternatives

In the video, Facebook says they currently have 30PB of cold storage at one facility and are already in the process of building another. They said that they should have 150PB of cold storage online shortly and that each cold storage facility is capable of holding 3EB or 3,000PB of cold storage.

A couple of years back at Hitachi in Japan, we were shown a Blu Ray optical disc library using 50GB discs. This was just a prototype but they were getting pretty serious about it then. We also saw an update of this at an analyst meeting at HDS, a year or so later. So there’s at least one storage company working on this technology.

Facebook, seems to have decided they were better off developing their own approach. It’s probably more dense/space efficient and maybe even more power efficient but to tell that would take some spec comparisons which aren’t available from Facebook or HDS just yet.

Why not magnetic tape?

I see these large storage repository sizes and wonder if Facebook might not be better off using magnetic tape. It has a much larger capacity and I believe magnetic tape (LTO or enterprise) would supply better volumetric (bytes/in**3) density than the Blu Ray cabinet they showed in the video.

Facebook said that BluRay discs had a 50 year lifetime.  I believe enterprise and LTO tape vendors say their cartridges have a 30 year lifetime. And that might be one consideration driving them to optical.

The reality is that new LTO technology is coming out every 2-3 years or so, and new drives read only 2 generations back and write only the current technology. With that quick a turnover, a data center would probably have to migrate data from old to new tape technology every decade or so before old tape drives go out of warranty.

I have not seen any Blu Ray technology roadmaps so it’s hard to make a comparison, but to date, PC based Blu Ray drives typically can read and write CDs, DVDs, and current Blu Ray disks (which is probably 4 to 5 generations back). So they have a better reputation for backward compatibility over time.

Tape technology roadmaps are so quick because tape competes with disk, which doubles capacity every 18 months or so. I am sure tape drive and media vendors would be happy not to upgrade their technology so fast but then disk storage would take over more and more tape storage applications.

If Blu Ray were to become a data center storage standard, as Facebook seems to want, I believe that Blu Ray technology would fall under similar competitive pressures from both disk and tape to upgrade optical technology at a faster rate. When that happens, it would be interesting to see how quickly optical drives stop supporting the backward compatibility that they currently support.


Photo Credit: [73/366] Grooves by Dwayne Bent [Ed. note, picture of DVD, not Blu Ray disc]



Tape vs. Disk, the saga continues

Inside a (Spectra Logic) T950 library by ChrisDag (cc) (from Flickr)
Inside a (Spectra Logic) T950 library by ChrisDag (cc) (from Flickr)

Was on a call late last month where Oracle introduced their latest generation T1000C tape system (media and drive) holding 5TB native (uncompressed) capacity. In the last 6 months I have been hearing about the coming of a 3TB SATA disk drive from Hitachi GST and others. And last month, EMC announced a new Data Domain Archiver, a disk only archive appliance (see my post on EMC Data Domain products enter the archive market).

Oracle assures me that tape density is keeping up if not gaining on disk density trends and capacity. But density or capacity are not the only issues causing data to move off of tape in today’s enterprise data centers.

“Dedupe Rulz”

A problem with the data density trends discussion is that it’s one dimensional (well literally it’s 2 dimensional). With data compression, disk or tape systems can easily double the density on a piece of media. But with data deduplication, the multiples start becoming more like 5X to 30X depending on frequency of full backups or duplicated data. And number’s like those dwarf any discussion of density ratios and as such, get’s everyone’s attention.

I can remember talking to an avowed tape enginerr, years ago and he was describing deduplication technology at the VTL level as being architecturally inpure and inefficient. From his perspective it needed to be done much earlier in the data flow. But what they failed to see was the ability of VTL deduplication to be plug-compatible with the tape systems of that time. Such ease of adoption allowed deduplication systems to build a beach-head and economies of scale. From there such systems have no been able to move up stream, into earlier stages of the backup data flow.

Nowadays, what with Avamar, Symantec Pure Disk and others, source level deduplication, or close by source level deduplication is a reality. But all this came about because they were able to offer 30X the density on a piece of backup storage.

Tape’s next step

Tape could easily fight back. All that would be needed is some system in front of a tape library that provided deduplication capabilities not just to the disk media but the tape media as well. This way the 30X density over non-deduplicated storage could follow through all the way to the tape media.

In the past, this made little sense because a deduplicated tape would require potentially multiple volumes in order to restore a particular set of data. However, with today’s 5TB of data on a tape, maybe this doesn’t have to be the case anymore. In addition, by having a deduplication system in front of the tape library, it could support most of the immediate data restore activity while data restored from tape was sort of like pulling something out of an archive and as such, might take longer to perform. In any event, with LTO’s multi-partitioning and the other enterprise class tapes having multiple domains, creating a structure with meta-data partition and a data partition is easier than ever.

“Got Dedupe”

There are plenty of places, that today’s tape vendors can obtain deduplication capabilities. Permabit offers Dedupe code for OEM applications for those that have no dedupe systems today. FalconStor, Sepaton and others offer deduplication systems that can be OEMed. IBM, HP, and Quantum already have tape libraries and their own dedupe systems available today all of which can readily support a deduplicating front-end to their tape libraries, if they don’t already.

Where “Tape Rulz”

There are places where data deduplication doesn’t work very well today, mainly rich media, physics, biopharm and other non-compressible big-data applications. For these situations, tape still has a home but for the rest of the data center world today, deduplication is taking over, if it hasn’t already. The sooner tape get’s on the deduplication bandwagon the better for the IT industry.


Of course there are other problems hurting tape today. I know of at least one large conglomerate that has moved all backup off tape altogether, even data which doesn’t deduplicate well (see my previous Oracle RMAN posts). And at least another rich media conglomerate that is considering the very same move. For now, tape has a safe harbor in big science, but it won’t last long.


SOHO backup options

© 2010 RDX Storage Alliance. All Rights Reserved. (From their website)
© 2010 RDX Storage Alliance. All Rights Reserved. (From their website)

I must admit, even though I have disparaged DVD archive life (see CDs and DVDs longevity questioned) I still backup my work desktops/family computers to DVD and DVDdl disks.  It’s cheap (on sale 100 DVDs cost about $30 and DVDdl ~2.5 that much) and it’s convenient (no need for additional software, outside storage fees, or additional drives).  For offsite backups I take the monthly backups and store them in a safety deposit box.

But my partner (and wife) said “Your time is worth something, every time you have to swap DVDs you could be doing something else.” (… like helping around the house.)

She followed up by saying “Couldn’t you use something that was start it and forget it til it was done.”

Well this got me to thinking (as well as having multiple media errors in my latest DVDdl full backup), there’s got to be a better way.

The options for SOHO (small office/home office) Offsite backups look to be as follows: (from sexiest to least sexy)

  • Cloud storage for backup – Mozy, Norton BackupGladinetNasuni, and no doubt many others can provide secure, cloud based backup of desktop, laptop data for Macs and Window systems.  Some of these would require a separate VM or server to connect to the cloud while others would not.  Using the cloud might require the office systems to be left on at nite but that would be a small price to pay to backup your data offsite.   Benefits to cloud storage approaches are that it would get the backups offsite, could be automatically scheduled/scripted to take place off-hours and would require no (or minimal) user intervention to perform.  Disadvantages to this approach is that the office systems would need to be left powered on, backup data is out of your control and bandwidth and storage fees would need to be paid.
  • RDX devices – these are removable NFS accessed disk storage which can support from 40GB to 640GB per cartridge. The devices claim 30yr archive life, which should be fine for SOHO purposes.  Cost of cartridges is probably RDX greatest issue BUT, unlike DVDs you can reuse RDX media if you want to.   Benefits are that RDX would require minimal operator intervention for anything less than 640GB of backup data, backups would be faster (45MB/s), and the data would be under your control.  Disadvantages are the cost of the media (640GB Imation RDX cartridge ~$310) and drives (?), data would not be encrypted unless encrypted at the host, and you would need to move the cartridge data offsite.
  • LTO tape – To my knowledge there is only one vendor out there that makes an iSCSI LTO tape and that is my friends at Spectra Logic but they also make a SAS (6Gb/s) attached LTO-5 tape drive.  It’s unclear which level of LTO technology is supported with the iSCSI drive but even one or two generations down would work for many SOHO shops.  Benefits of LTO tape are minimal operator intervention, long archive life, enterprise class backup technology, faster backups and drive data encryption.  Disadvantages are the cost of the media ($27-$30 for LTO-4 cartridges), drive costs(?), interface costs (if any) and the need to move the cartridges offsite.  I like the iSCSI drive because all one would need is a iSCSI initiator software which can be had easily enough for most desktop systems.
  • DAT tape – I thought these were dead but my good friend John Obeto informed me they are alive and well.  DAT drives support USB 2.0, SAS or parallel SCSI interfaces. Although it’s unclear whether they have drivers for Mac OS/X, Windows shops could probably use them without problem. Benefits are similar to LTO tape above but not as fast and not as long a archive life.  Disadvantages are cartridge cost (320GB DAT cartridge ~$37), drive costs (?) and one would have to move the media offsite.
  • (Blu-ray, Blu-ray dl), DVD, or DVDdl – These are ok but their archive life is miserable (under 2yrs for DVDs at best, see post link above). Benefits are they’res very cheap to use, lowest cost removable media (100GB of data would take ~22 DVDs or 12 DVDdls which at $0.30/ DVD or $0.75 for DVDdl thats  ~$6.60 to $9 per backup), and lowest cost drive (comes optional on most desktops today). Disadvantages are high operator intervention (to swap out disks), more complexity to keep track of each DVDs portion of the backup, more complex media storage (you have a lot more of it), it takes forever (burning 7.7GB to a DVDdl takes around an hour or ~2.1MB/sec.), data encryption would need to be done at the host, and one has to take the media offsite.  I don’t have similar performance data for using Blu-ray  for backups other than Blu-ray dl media costs about $11.50 each (50GB).

Please note this post only discusses Offsite backups. Many SOHOs do not provide offsite backup (risky??) and for online backups I use a spare disk drive attached to every office and family desktop.

Probably other alternatives exist for offsite backups, not the least of which is NAS data replication.  I didn’t list this as most SOHO customers are unlikely to have a secondary location where they could host the replicated data copy and the cost of a 2nd NAS box would need to be added along with the bandwidth between the primary and secondary site.  BUT for those sophisticated SOHO customers out there already using a NAS box for onsite shared storage maybe data replication might make sense. Deduplication backup appliances are another possibility but suffer similar disadvantages to NAS box replication and are even less likely to be already used by SOHO customers.


Ok where to now.  Given all this I M hoping to get a Blu-ray dl writer in my next iMac.  Let’s see that would cut my DVDdl swaps down by ~3.2X for single layer and ~6.5X for dl Blu-ray.  I could easily live with that until I quadrupled my data storage, again.

Although an iSCSI LTO-5 tape transport would make a real nice addition to the office…


The problems with digital audio archives

ldbell15 by Zyada (cc) (from Flickr)
ldbell15 by Zyada (cc) (from Flickr)

A recent article in Rolling Stone (File Not Found: The Record Industry’s Digital Storage Crisis) laments the fact that digital recordings can go out of service due to format changes, plugin changes, and/or files not being readable (file not found).

In olden days, multi-track masters were recorded on audio tape and kept in vaults.  Audio tape formats never seemed to change or at least changed infrequently, and thus, re-usable years or decades after being recorded.  And the audio tape drives seemed to last forever.

Digital audio recordings on the other hand, are typically stored in book cases/file cabinets/drawers, on media that can easily become out-of-date technology (i.e., un-readable) and in digital formats that seem to change with every new version of software.

Consumer grade media doesn’t archive very well

The article talks about using hard drives for digital recordings and trying to read them decades after they were recorded.  I would be surprised if they still spin up (due to stiction) let alone still readable.  But even if these were CDs or DVDs, the lifetime of consumer grade media is not that long, maybe a couple of years at best, if treated well and if abused by writing on them or by bad handling, it’s considerably less than that.

Digital audio formats change frequently

The other problem with digital audio recordings is that formats go out of date.  I am no expert but let’s take Apple’s Garage Band as an example.  I would be surprised if 15 years down the line that a 2010 Garage Band session recorded today was readable/usable with Garage Band 2025, assuming it even existed.  Sounds like a long time but it’s probably nothing for popular music coming out today.

Solutions to digital audio media problems

Audio recordings must use archive grade media if it’s to survive for longer than 18-36 months.  I am aware of archive grade DVD disks but have never tested any, so cannot speak to their viability in this application.  However, for an interesting discussion on archive quality CD&DVD media see How to choose CD/DVD archival media. But, there are other alternatives.

Removable data center class archive media today includes magnetic tape, removable magnetic disks or removable MO disks.

  • Magnetic tape – LTO media vendors specify archive life on the order of 30 years, however this assumes a drive exists that can read the media.  The LTO consortium states that current generation drives will read back two generations (LTO-5 drive today reads LTO-4 and LTO-3 media) and write back one generation (LTO-5 drive can write on LTO-4 media [in LTO-4 format]).  With LTO generations coming every 2 years or so, it would only take 6 years for a LTO volume, recorded today to be unreadable by current drives.  Naturally, one could keep an old drive around but maintenance/service would no longer be available for it after a couple of years.  LTO drives are available from a number of vendors.
  • Magnetic disk – The RDX Storage Alliance claims a media archive life of 30 years but I wonder whether a RDX drive would exist that could read it and the other question is how archive life was validated. Today’s removable disk typically imitates a magnetic tape drive/format.  The most prominent removable disk vendor is ProStor Systems but there are others.
  • Magneto-optical (MO) media – Plasmon UDO claims a media life of 50+ years for their magneto-optical media.  UDO has been used for years to record check images, medical information and other data.  Nonetheless,  recently UDO technology has not been able to keep up with other digital archive solutions and have gained a pretty bad rap for usability problems.  However, they plan to release a new generation of UDO product line in 2010 which may shake things up if it arrives and can address their usability issues.

Finally, one could use non-removable, high density disk drives and migrate the audio data every 2-3 years to new generation disks.  This would keep the data readable and continuously accessible.  Modern storage systems with RAID and other advanced protection schemes can protect data from any single and potentially double drive failure but as drives age, their error rate goes up.  This is why the data needs to be moved to new disks periodically.  Naturally, this is more frequently than magnetic tape, but given disk drive usability and capacity gains, might make sense in certain applications.

As for removable USB sticks – unclear what the archive life is for these consumer devices but potentially some version that went after the archive market might make sense.  It would need to be robust, have a long archive life and be cheap enough to compete with all the above.  I just don’t see anything here yet.

Solutions to digital audio format problems

There needs to be an XML-like description of a master recording that reduces everything to a more self-defined level which describes the hierarchy of the recording, and provides object buckets for various audio tracks/assets.  Plugins that create special effects would need to convert their effects to something akin to a MPEG-like track that could be mixed with the other tracks, surrounded by meta-data describing where it starts, ends and other important info.

Baring that, some form of standardization on a master recording format would work.  Such a standard could be supported by all major recording tools and would allow a master recording to be exported and imported across software tools/versions.  As this format evolved, migration/conversion products could be supplied to upgrade old formats to new ones.

Another approach is to have some repository for current master audio recording formats.  As software packages go out of date/business, their recording format could be stored in some “format repository”, funded by the recording industry and maintained in perpetuity.  Plug-in use would need to be documented similarly.  With a repository like this around and “some amount” of coding, no master recording need be lost to out-of-date software formats.

Nonetheless, If your audio archive needs to be migrated periodically, it be a convenient time to upgrade the audio format as well.


I have written about these problems before in a more general sense (see Today’s data and the 1000 year archive) but the recording industry seems to be “leading edge” for these issues. When Producer T Bone Burnett testifies at a hearing that “Digital is a feeble storage medium” it’s time to step up and take action.

Digital storage is no more feeble than analog storage – they each have their strengths and weaknesses.  Analog storage has gone away because it couldn’t keep up with digital recording densities, pricing, and increased functionality.  Just because data is recorded digitally doesn’t mean it has to be impermanent, hard to read 15-35 years hence, or in formats that are no longer supported.  But it does take some careful thought on what storage media you use and on how you format your data.


Primary storage compression can work

Dans la nuit des images (Grand Palais) by dalbera (cc) (from flickr)
Dans la nuit des images (Grand Palais) by dalbera (cc) (from flickr)

Since IBM’s announced their intent to purchase StorWize there has been much discussion on whether primary storage data compression can be made to work.  As far as I know StorWize only offered primary storage compression for file data but there is nothing that prohibits doing something similar for block storage as long as you have some control over how blocks are laid down on disk.

Although secondary block  data compression has been around for years in enterprise tape and more recently with some deduplication appliances, primary storage compression pre-dates secondary storage compression.  STK delivered primary storage data compression with Iceberg in the early 90’s but it wasn’t until a couple of years later that they introduced compression on tape.

In both primary and secondary storage, data compression works to reduce the space needed to store data.  Of course, not all data compresses well, most notably image data (as it’s already compressed) but compression ratios of 2:1 were common for primary storage of that time and are normal for today’s secondary storage.  I see no reason why such ratios couldn’t be achieved for current primary storage block data.

Implementing primary block storage data compression

There is significant interest in implementing deduplication for primary storage as NetApp has done but supporting data compression is not much harder.  I believe much of the effort to deduplicate primary storage lies in creating a method to address partial blocks out of order, which I would call data block virtual addressing which requires some sort of storage pool.  The remaining effort to deduplicate data involves implementing the chosen (dedupe) algorithm, indexing/hashing, and other administrative activities.  These later activities aren’t readily transferable to data compression but the virtual addressing and space pooling should be usable by data compression.

Furthermore, block storage thin provisioning requires some sort of virtual addressing as does automated storage tiering.  So in my view, once you have implemented some of these advanced capabilities, implementing data compression is not that big a deal.

The one question that remains is does one implement compression with hardware or software (see Better storage through hardware for more). Considering that most deduplication is done via software today it seems that data compression in software should be doable.  The compression phase could run in the background sometime after the data has been stored.  Real time decompression using software might take some work, but would cost considerably less than any hardware solution.  Although the intensive bit fiddling required to perform data compression/decompression may argue for some sort of hardware assist.

Data compression complements deduplication

The problem with deduplication is that it needs duplicate data.  This is why it works so well for secondary storage (backing up the same data over and over) and for VDI/VMware primary storage (with duplicated O/S data).

But data compression is an orthogonal or complementary technique which uses the inherent redundancy in information to reduce storage requirements.  For instance, something like LZ compression takes advantage of the fact that in text some letters occur more often than others (see letter frequency). For instance, in English, ‘e’, ‘t’, ‘a’, ‘o’, ‘i’, and ‘n, represent over 50% of the characters in most text documents.  By using shorter bit combinations to encode these letters one can reduce the bit-length of any (English) text string substantially.  Another example is run length encoding which takes any repeated character and substitutes a trigger character, the character itself, and a count of the number of repetitions for the repeated string.

Moreover, the nice thing about data compression is that all these techniques can be readily combined to generate even better compression rates.  And of course compression could be applied after deduplication to reduce storage footprint even more.

Why would any vendor compress data?

For a couple of reasons:

  • Compression not only reduces storage footprint but with hardware assist it can also increase storage throughput. For example, if 10GB of data compresses down to 5GB, it should take ~1/2 the time to read.
  • Compression reduces the time it would take time to clone, mirror or replicate.
  • Compression increases the amount of data that could be stored which should incentivise them to pay more for your storage.

In contrast, with data compression vendors might may sell less storage.  But the advantages of enterprise storage is in the advanced functionality/features and higher reliability/availability/performance that are available.  I see data compression as just another advantages to enterprise class storage and as a feature, the user could enable or disable it and see how well it works for there data.

What do you think?

CDs and DVDs longevity questioned

DVD-R read/write side (from Wikipedia.org)
DVD-R read/write side (from Wikipedia.org)

In a recent article from BBC on Should you store treasured data on (optical) disk the conclusion was that CDs and DVDs have significantly worse archive life than advertised or even suspected until recently.  The study done by the French National Centre for Scientific Research discovered that the reliability of a few optical disks was just over one year and most “rarely lasted longer than five to 10 years” although they were advertised to last significantly more.

There was not much detail in the BBC article and searching (in English) for the original research yielded nothing pertaining to the topic.   However, the article did say that the centre used accelerated life testing with heat, water vapor and light (standard IT industry practice) to determine point of failure and that products under the same brand had significant archive life variability due to multiple manufacturers.  They also stated that branding the discs might be impacting longevity as well. And that it appeared that the more than seven miles of (probably DVD) data recorded on the discs is deteriating faster than anticipated.

As a result, they suggested that data on optical disks should be copied every two to three years and maybe as time moves on, this can be done less frequently assuming optical disk lifespans improve.  Also important data should be spread across multiple storage formats.

The case for (IT) tape in video archives

Nonetheless, the article did mention that a 52 minute documentary typically requires about 500GB of high definition video to be recorded and at the moment that video is normally stored on data (tape) cassettes and hard drives.  In my experience these (video) tapes were specific to the recording equipment vendor, i.e. Panasonic, Sony, or others and as such, relatively expensive.  But nowadays, this data can also be stored on LTO or other IT tapes.  In contrast to the above, LTO tape has an archival storage life of around 30 years (depending on vendor) and can be had at reasonable cost.

Also, in the past I was aware of a number of TV broadcasters that had an archive of finished broadcasts residing only on DVDs.  They typically took one additional copy of a DVD and stored them both in their desks or file cabinets.  Many of these people will be very surprised when five years down the line, they go to access their archived broadcasts and find that they can no longer be read.  Of course, I have made the same mistake with my family video archive stored on DVDs.

Video archives whether of raw video or finished broadcasts require large capacity, sequentially accessed storage which seems ideal for automated LTO or other magnetic tape storage.  By using IT tape data storage for video archives, one can benefit from technology advances in density and throughput that happen every couple of years, benefit from volume manufacturing available to IT product manufacturers, and benefit from a significantly longer archive life.

Now if I can just find a USB LTO tape drive that works on the Mac for my home videos and family backups I would feel much better, …

Protecting the Yottabyte archive

blinkenlights by habi (cc) (from flickr)
blinkenlights by habi (cc) (from flickr)

In a previous post I discussed what it would take to store 1YB of data in 2015 for the National Security Agency (NSA). Due to length, that post did not discuss many other aspects of the 1YB archive such as ingest, index, data protection, etc. Thus, I will attempt to cover each of these in turn and as such, this post will cover some of the data protection aspects of the 1YB archive and its catalog/index.

RAID protecting 1YB of data

Protecting the 1YB archive will require some sort of parity protection. RAID data protection could certainly be used and may need to be extended to removable media (RAID for tape), but that would require somewhere in the neighborhood of 10-20% additional storage (RAID5 across 10 to 5 tape drives). It’s possible with Reed-Solomon encoding and using RAID6 that we could take this down to 5-10% of additional storage (RAID 6 for a 40 to a 20 wide tape drive stripe). Possibly other forms of ECC (such as turbo codes) might be usable in a RAID like configuration which would give even better reliability with less additional storage.

But RAID like protection also applies to the data catalog and indexes required to access the 1YB archive of data. Ditto for the online data itself while it’s being ingested, indexed, or readback. For the remainder of this post I ignore the RAID overhead but suffice it to say with today’s an additional 10% storage for parity will not change this discussion much.

Also in the original post I envisioned a multi-tier storage hierarchy but the lowest tier always held a copy of any files residing in the upper tiers. This would provide some RAID1 like redundancy for any online data. This might be pretty usefull, i.e., if a file is of high interest, it could have been accessed recently and therefore resides in upper storage tiers. As such, multiple copies of interesting files could exist.

Catalog and indexes backups for 1YB archive

IMHO, RAID or other parity protection is different than data backup. Data backup is generally used as a last line of defense for hardware failure, software failure or user error (deleting the wrong data). It’s certainly possible that the lowest tier data is stored on some sort of WORM (write once read many times) media meaning it cannot be overwritten, eliminating one class of user error.

But this presumes the catalog is available and the media is locatable. Which means the catalog has to be preserved/protected from user error, HW and SW failures. I wrote about whether cloud storage needs backup in a prior post and feel strongly that the 1YB archive would also require backups as well.

In general, backup today is done by copying the data to some other storage and keeping that storage offsite from the original data center. At this amount of data, most likely the 2.1×10**21 of catalog (see original post) and index data would be copied to some form of removable media. The catalog is most important as the other two indexes could potentially be rebuilt from the catalog and original data. Assuming we are unwilling to reindex the data, with LTO-6 tape cartridges, the catalog and index backups would take 1.3×10**9 LTO-6 cartridges (at 1.6×10**12 bytes/cartridge).

To back up this amount of data once per month would take a gaggle of tape drives. There are ~2.6×10**6 seconds/month and each LTO-6 drive can transfer 5.4×10**8 bytes/sec or 1.4X10**15 bytes/drive-month but we need to backup 2.1×10**21 bytes of data so we need ~1.5×10**6 tape transports. Now tapes do not operate 100% of the time because when a cartridge becomes full it has to be changed out with an empty one, but this amounts to a rounding error at these numbers.

To figure out the tape robotics needed to service 1.5×10**6 transports we could use the latest T-finity tape library just announced by Spectra Logic . The T-Finity supports 500 tape drives and 122,000 tape cartridges, so we would need 3.0×10**3 libraries to handle the drive workload and about 1.1×10**4 libraries to store the cartridge set required, so 11,000 T-finity libraries would suffice. Presumably, using LTO-7 these numbers could be cut in half ~5,500 libraries, ~7.5×10**5 transports, and 6.6×10**8 cartridges.

Other removable media exist, most notably the Prostor RDX. However RDX roadmap info out to the next generation are not readily available and high-end robotics are do not currently support RDX. So for the moment tape seems the only viable removable backup for the catalog and index for the 1YB archive.

Mirroring the data

Another approach to protecting the data is to mirror the catalog and index data. This involves taking the data and copying it to another online storage repository. This doubles the storage required (to 4.2×10**21 bytes of storage). Replication doesn’t easily protect from user error but is an option worthy of consideration.

Networking infrastructure needed

Whether mirroring or backing up to tape, moving this amount of data will require substantial networking infrastructure. If we assume that in 2105 we have 32GFC (32 gb/sec fibre channel interfaces). Each interface could potentially transfer 3.2GB/s or 3.2×10**9 bytes/sec. Mirroring or backing up 2.1×10**21 bytes over one month will take ~2.5×10**6 32GFC interfaces. Probably should have twice this amount of networking just to not have any one be a bottleneck so 5×10**6 32GFC interfaces should work.

As for switches, the current Brocade DCX supports 768 8GFC ports and presumably similar port counts will be available in 2015 to support 32GFC. In addition if we assume at least 2 ports per link, we will need ~6,500 fully populated DCX switches. This doesn’t account for multi-layer switches and other sophisticated switch topologies but could be accommodated with another factor of 2 or ~13,000 switches.

Hot backups require journals

This all assumes we can do catalog and index backups once per month and take the whole month to do them. Now storage today normally has to be taken offline (via snapshot or some other mechanism) to be backed up in a consistent state. While it’s not impossible to backup data that is concurrently being updated it is more difficult. In this case, one needs to maintain a journal file of the updates going on while the data is being backed up and be able to apply the journaled changes to the data backed up.

For the moment I am not going to determine the storage requirements for the journal file required to cover the catalog transactions for a month, but this is dependent on the change rate of the catalog data. So it will necessarily be a function of the index or ingest rate of the 1YB archive to be covered in a future post.

Stay tuned, I am just having too much fun to stop.

Quantum OEMs esXpress VM Backup SW

Quantum announced today that they are OEMing esXpress software (from PHD Virtual) to better support VMware VM backups (see press release) . This software schedules VMware snapshots of VMs and can then transfer the VM snapshot (backup) data directly to a Quantum DXI storage device.

One free “Professional” esXpress license will ship with each DXI appliance which allows for up to 4-esXpress virtual backup appliance (VBA) virtual machines to run in a single VMware physical server. An “Enterprise” license can be purchased for $1850 which allows for up to 16-esXpress VBA virtual machines to run on a single VMware physical server. More Professional licenses can be purchased for $950 each. The free Professional license also comes with free installation services from Quantum.

Additional esXpress VBAs can be used to support more backup data throughput from a single physical server. The VBA backup activity is a scheduled process and as such, when completed the VBA can be “powered” down to save VMware server resources. Also as VBAs are just VMs they fully support VMware Vmotion, DRS, and HA capabilities that are available from VMware. However using any of these facilities to move a VBA to another physical server may require additional licensing.

The esXpress software eliminates the need for a separate VCB (VMware Consolidated Backup) proxy server and provides a direct interface to support Quantum DXI deduplicated storage for VM backups. This should simplify backup processing for VMware VMs using DXI archive storage.

Quantum also announced today a new key manager, the Scalar Key Manager for Quantum LTO tape encryption which has an integrated GUI with Quantum’s tape automation products. This allows a tape automation manager a single user interface to support tape automation and tape security/encryption. A single point of management should simplify the use of Quantum LTO tape encryption.