Functional Fusion? by Cain Novocaine (cc) (from Flickr)
One can only be perplexed by the seemingly overwelming adoption of server virtualization and contrast that with the ho-hum, almost underwelming adoption of storage virtualization. Why is there this significant a difference?
I think the problem is partly due to the lack of an common understanding of storage performance utilization.
Why server virtualization succeeded
One significant driver of server virtualization is the precipitous drop in server utilization that occurred over the last decade when running single applications on a physical server. It was nothing to see real processor utilization of less than 10% and consequently it was easy to envision that executing 5-10 applications on the single server. And what’s more each new generation of server kept getting more powerful, handling double the MIPs every 18 months or so driven by Moore’s law.
The other factor was that application workloads weren’t increasing that much. Yes new applications would come online but they seldom consumed an inordinate amount of MIPs and were often similar to what was already present. So application processing growth while not flatlining, was expanding at a relatively slow speed.
Why storage virtualization has failed
Data on the other hand continues its never ending exponential growth. Doubling every 3-5 years or less. And the fact that you have more data, almost always requires more storage hardware to support the IOPs being required to support it.
In the past the storage IOP rates was intrinsically tied to the number of disk heads available to service the load. Although disk performance grew it wasn’t doubling every 18 months, and real per disk performance was actually going down over time, measured as the amount of IOPS per GB.
This drove proliferation of disk spindles and as such, storage subsystems in the data center. Storage virtualization couldn’t reduce the number of spindles required to support the workload.
Thus, if you look at storage performance from the perspective of % IOPS one could support per disk, most sophisticated systems were running anywhere from 75% to 150% (based on DRAM caching).
Paradigm shift ahead
But SSDs can change this dynamic considerably. A typical SSD can sustain 10-100K IOPs and there is some liklihood that this will increase with each generation that comes out but the application requirements will not increase as fast. Hence, , there is a high liklihood that normal data center utilisation of SSD storage perfomance will start to drop below 50% or more, when that happens. -torage virtualization may start to make a lot more sense.
Maybe when (SSD) data storage starts moving more in line with Moore’s law, storage virtualization will become a more dominant paradigm for data center storage use.
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Any bets on who the VMware of storage virtualization will be?
Model of graphene structure by CORE-Materials (cc) (from Flickr)
I have been thinking about writing a post on “Is Flash Dead?” for a while now. Well at least since talking with IBM research a couple of weeks ago on their new memory technologies that they have been working on.
As we have discussed before, NAND flash memory has some serious limitations as it’s shrunk below 11nm or so. For instance, write endurance plummets, memory retention times are reduced and cell-to-cell interactions increase significantly.
These issues are not that much of a problem with today’s flash at 20nm or so. But to continue to follow Moore’s law and drop the price of NAND flash on a $/Gb basis, it will need to shrink below 16nm. At that point or soon thereafter, current NAND flash technology will no longer be viable.
Other non-NAND based non-volatile memories
That’s why IBM and others are working on different types of non-volatile storage such as PCM (phase change memory), MRAM (magnetic RAM) , FeRAM (Ferroelectric RAM) and others. All these have the potential to improve general reliability characteristics beyond where NAND Flash is today and where it will be tomorrow as chip geometries shrink even more.
IBM seems to be betting on MRAM or racetrack memory technology because it has near DRAM performance, extremely low power and can store far more data in the same amount of space. It sort of reminds me of delay line memory where bits were stored on a wire line and read out as they passed across a read/write circuit. Only in the case of racetrack memory, the delay line is etched in a silicon circuit indentation with the read/write head implemented at the bottom of the cleft.
Graphene as the solution
Then along comes Graphene based Flash Memory. Graphene can apparently be used as a substitute for the storage layer in a flash memory cell. According to the report, the graphene stores data using less power and with better stability over time. Both crucial problems with NAND flash memory as it’s shrunk below today’s geometries. The research is being done at UCLA and is supported by Samsung, a significant manufacturer of NAND flash memory today.
Current demonstration chips are much larger than would be useful. However, given graphene’s material characteristics, the researchers believe there should be no problem scaling it down below where NAND Flash would start exhibiting problems. The next iteration of research will be to see if their scaling assumptions can hold when device geometry is shrunk.
The other problem is getting graphene, a new material, into current chip production. Current materials used in chip manufacturing lines are very tightly controlled and building hybrid graphene devices to the same level of manufacturing tolerances and control will take some effort.
So don’t look for Graphene Flash Memory to show up anytime soon. But given that 16nm chip geometries are only a couple of years out and 11nm, a couple of years beyond that, it wouldn’t surprise me to see Graphene based Flash Memory introduced in about 4 years or so. Then again, I am no materials expert, so don’t hold me to this timeline.
EMC World keynote stage, storage, vblocks, and cloud...
EMC announced today a couple of new twists on the flash/SSD storage end of the product spectrum. Specifically,
They now support all flash/no-disk storage systems. Apparently they have been getting requests to eliminate disk storage altogether. Probably government IT but maybe some high-end enterprise customers with low-power, high performance requirements.
They are going to roll out enterprise MLC flash. It’s unclear when it will be released but it’s coming soon, different price curve, different longevity (maybe), but brings down the cost of flash by ~2X.
EMC is going to start selling server side Flash. Using storage FAST like caching algorithms to knit the storage to the server side Flash. Unclear what server Flash they will be using but it sounds a lot like a Fusion-IO type of product. How well the server cache and the storage cache talks is another matter. Chuck Hollis said EMC decided to redraw the boundary between storage and server and now there is a dotted line that spans the SAN/NAS boundary and carves out a piece of the server which is sort of on server caching.
Interesting to say the least. How well it’s tied to the rest of the FAST suite is critical. What happens when one or the other loses power, as Flash is non-volatile no data would be lost but the currency of the data for shared storage may be another question. Also having multiple servers in the environment may require cache coherence across the servers and storage participating in this data network!?
Some teaser announcements from Joe’s keynote:
VPLEX asynchronous, active active supporting two datacenter access to the same data over 1700Km away Pittsburgh to Dallas.
New Isilon record scalability and capacity the NL appliance. Can now support a 15PB file system, with trillions of files in it. One gene sequencer says a typical assay generates 500M objects/files…
Embracing Hadoop open source products so that EMC will support Hadoop distro in an appliance or software only solution
Pat G also showed EMC Greenplum appliance searching a 8B row database to find out how many products have been shipped to a specific zip code…
Had a talk the other week with an storage executive about SSD and NAND cost trends. It seemed that everyone thought that $/GB for SSD was going to overtake (be less costly) than enterprise class disk sometime in 2013. But it appeared that NAND costs weren’t coming down as fast as anticipated and now this was going to take longer than expected.
A couple of other things are going on in the enterprise disk market that are also having an effect on the relative advantage of SSDs over disks. Probably, most concerning to SSD market is enterprise storage’s new penchant for sub-LUN tiering.
Automated sub-LUN storage tiering
The major storage vendors all currently support some form of automated storage tiering for SSD storage (NetApp’s Flash Cache does this differently but the impact on NAND storage requirements is arguably similar). Presumably, such tiering should take better advantage of any amount of SSD/NAND storage available to a storage system.
Prior to automated sub-LUN storage tiering, one had to move a whole LUN to SSDs to take advantage of its speed. However, I/O requests or access are not necessarily at the same intensity for all blocks of a LUN. So one would typically end up with an SSD LUN with a relatively few blocks being heavily accessed while the vast majority of its blocks would not be being hit that much. We paid the high price of SSD LUNs gladly to get the high performance for those few blocks that really needed it.
However, with sub-LUN tiering or NAND caching, one no longer has to move all the blocks of a LUN into NAND storage to gain its benefits. One can now just have the system identify those select blocks which need high performance and move those blocks and those blocks only to NAND storage. The net impact of sub-LUN tiering or NAND caching is that one should require less overall NAND storage to obtain the same performance as one had previously with SSDs alone.
On the other hand, some would say that making the performance advantages of NAND be available at a lower overall cost might actually increase the overall amount of NAND shipments. Also with automated sub-LUN tiering in place, this removes all the complexity needed previously to identify which LUNs needed higher performance. Reducing such complexity should increase SSD or NAND market penetration.
Nonetheless, I feel that given todays price differential of SSDs over enterprise disk, the people buying SSDs today have a very defined need for speed and would have paid the price anyways for SSD storage. Anything we do to make satisfying that need with less SSD or NAND storage should reduce the amount of SSDs shipped today.
But getting back to that price crossover point, as the relative price of NAND on $/GB comes down, having an easy way to take advantage of its better performance should increase its market adoption, even faster than price would do alone.
A head assembly on a Seagate disk drive by Robert Scoble (cc) (from flickr)
Yesterday, it was announced that Hitachi General Storage Technologies (HGST) is being sold to Western Digital for $4.3B and after that there was much discussion in the tweeterverse about the end of enterprise disk as we know it. Also, last week I was at a dinner at an analyst meeting with Hitachi, where the conversation turned to when disks will no longer be available. This discussion was between Mr. Takashi Oeda of Hitachi RSD, Mr. John Webster of Evaluator group and myself.
Why SSDs will replace disks
John was of the opinion that disks would stop being economically viable in about 5 years time and will no longer be shipping in volume, mainly due to energy costs. Oeda-san said that Hitachi had predicted that NAND pricing on a $/GB basis would cross over (become less expensive than) 15Krpm disk pricing sometime around 2013. Later he said that NAND pricing had not come down as fast as projected and that it was going to take longer than anticipated. Note that Oeda-san mentioned density price cross over for only 15Krpm disk not 7200rpm disk. In all honesty, he said SATA disk would take longer, but he did not predict when
I think both arguments are flawed:
Energy costs for disk drives drop on a Watts/GB basis every time disk density increases. So the energy it takes to run a 600GB drive today will likely be able to run a 1.2TB drive tomorrow. I don’t think energy costs are going to be the main factor to drives disks out of the enterprise.
Density costs for NAND storage are certainly declining but cost/GB is not the only factor in technology adoption. Disk storage has cost more than tape capacity since the ’50s, yet they continue to coexist in the enterprise. I contend that disks will remain viable for at least the next 15-20 years over SSDs, primarily because disks have unique functional advantages which are vital to enterprise storage.
Most analysts would say I am wrong, but I disagree. I believe disks will continue to play an important role in the storage hierarchy of future enterprise data centers.
NAND/SSD flaws from an enterprise storage perspective
All costs aside, NAND based SSDs have serious disadvantages when it comes to:
Data retention – the problem with NAND data cells is that they can only be written so many times before they fail. And as NAND cells become smaller, this rate seems to be going the wrong way, i.e, today’s NAND technology can support 100K writes before failure but tomorrow’s NAND technology may only support 15K writes before failure. This is not a beneficial trend if one is going to depend on NAND technology for the storage of tomorrow.
Sequential access – although NAND SSDs perform much better than disk when it comes to random reads and less so, random writes, the performance advantage of sequential access is not that dramatic. NAND sequential access can be sped up by deploying multiple parallel channels but it starts looking like internal forms of wide striping across multiple disk drives.
Unbalanced performance – with NAND technology, reads operate quicker than writes. Sometimes 10X faster. Such unbalanced performance can make dealing with this technology more difficult and less advantageous than disk drives of today with much more balanced performance.
None of these problems will halt SSD use in the enterprise. They can all be dealt with through more complexity in the SSD or in the storage controller managing the SSDs, e.g., wear leveling to try to prolong data retention, multi-data channels for sequential access, etc. But all this additional complexity increases SSD cost, and time to market.
SSD vendors would respond with yes it’s more complex, but such complexity is a one time charge, mostly a one time delay, and once done, incremental costs are minimal. And when you come down to it, today’s disk drives are not that simple either with defect skipping, fault handling, etc.
So why won’t disk drives go away soon. I think other major concern in NAND/SSD ascendancy is the fact that the bulk NAND market is moving away from SLC (single level cell or bit/cell) NAND to MLC (multi-level cell) NAND due to it’s cost advantage. When SLC NAND is no longer the main technology being manufactured, it’s price will not drop as fast and it’s availability will become more limited.
Some vendors also counter this trend by incorporating MLC technology into enterprise SSDs. However, all the problems discussed earlier become an order of magnitude more severe with MLC NAND. For example, rather than 100K write operations to failure with SLC NAND today, it’s more like 10K write operations to failure on current MLC NAND. The fact that you get 2 to 3 times more storage per cell with MLC doesn’t help that much when one gets 10X less writes per cell. And the next generation of MLC is 10X worse, maybe getting on the order of 1000 writes/cell prior to failure. Similar issues occur for write performance, MLC writes are much slower than SLC writes.
So yes, raw NAND may become cheaper than 15Krpm Disks on a $/GB basis someday but the complexity to deal with such technology is also going up at an alarming rate.
Why disks will persist
Now something similar can be said for disk density, what with the transition to thermally assisted recording heads/media and the rise of bit-patterned media. All of which are making disk drives more complex with each generation that comes out. So what allows disks to persist long after $/GB is cheaper for NAND than disk:
Current infrastructure supports disk technology well in enterprise storage. Disks have been around so long, that storage controllers and server applications have all been designed around them. This legacy provides an advantage that will be difficult and time consuming to overcome. All this will delay NAND/SSD adoption in the enterprise for some time, at least until this infrastructural bias towards disk is neutralized.
Disk technology is not standing still. It’s essentially a race to see who will win the next generations storage. There is enough of an eco-system around disk that will keep pushing media, heads and mechanisms ever forward into higher densities, better throughput, and more economical storage.
However, any infrastructural advantage can be overcome in time. What will make this go away even quicker is the existance of a significant advantage over current disk technology in one or more dimensions. Cheaper and faster storage can make this a reality.
Moreover, as for the ecosystem discussion, arguably the NAND ecosystem is even larger than disk. I don’t have the figures but if one includes SSD drive producers as well as NAND semiconductor manufacturers the amount of capital investment in R&D is at least the size of disk technology if not orders of magnitude larger.
Disks will go extinct someday
So will disks become extinct, yes someday undoubtedly, but when is harder to nail down. Earlier in my career there was talk of super-paramagnetic effect that would limit how much data could be stored on a disk. Advances in heads and media moved that limit out of the way. However, there will come a time where it becomes impossible (or more likely too expensive) to increase magnetic recording density.
I was at a meeting a few years back where a magnetic head researcher predicted that such an end point to disk density increase would come in 25 years time for disk and 30 years for tape. When this occurs disk density increase will stand still and then it’s a certainty that some other technology will take over. Because as we all know data storage requirements will never stop increasing.
I think the other major unknown is other, non-NAND semiconductor storage technologies still under research. They have the potential for unlimited data retention, balanced performance and sequential performance orders of magnitude faster than disk and can become a much more functional equivalent of disk storage. Such technologies are not commercially available today in sufficient densities and cost to even threaten NAND let alone disk devices.
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So when do disks go extinct. I would say in 15 to 20 years time we may see the last disks in enterprise storage. That would give disks an almost an 80 year dominance over storage technology.
But in any event I don’t see disks going away anytime soon in enterprise storage.
I don’t know much about O/S drivers but I do know lots about storage interfaces. One thing that’s apparent from yesterday’s announcement from Intel is that Fibre Channel over Ethernet (FCoE) has taken another big leap forward.
Chad Sakac’s chart of FC vs. Ethernet target unit shipments (meaning, storage interface types, I think) clearly indicate a transition to ethernet is taking place in the storage industry today. Of course Ethernet targets can be used for NFS, CIFS, Object storage, iSCSI and FCoE so this doesn’t necessarily mean that FCoE is winning the game, just yet.
The advantage of FC, and iSCSI for that matter, is that every server, every OS, and just about every storage vendor in the world supports them. Also there are plethera of economical, fabric switches available from multiple vendors that can support multi-port switching with high bandwidth. And there many support matrixes, identifying server-HBAs, O/S drivers for those HBA’s and compatible storage products to insure compatibility. So there is no real problem (other than wading thru the support matrixes) to implementing either one of these storage protocols.
Enter Open-FCoE, the upstart
What’s missing from 10GBE FCoE is perhaps a really cheap solution, one that was universally available, using commodity parts and could be had for next to nothing. The new Open-FCoE drivers together with the Intels x520 10GBE NIC has the potential to answer that need.
But what is it? Essentially Intel’s Open-FCoE is an O/S driver for Windows and Linux and a 10GBE NIC hardware from Intel. It’s unclear whether Intel’s Open-FCoE driver is a derivative of the Open-FCoe.org’s Linux driver or not but either driver works to perform some of the FCoE specialized functions in software rather than hardware as done by CNA cards available from other vendors. Using server processing MIPS rather than ASIC processing capabilities should make FCoE adoption in the long run, even cheaper.
What about performance?
The proof of this will be in benchmark results but it’s quite possible to be a non-issue. Especially, if there is not a lot of extra processing involved in a FCoE transaction. For example, if Open-FCoE only takes let’s say 2-5% of server MIPS and bandwidth to perform the added FCoE frame processing then this might be in the noise for most standalone servers and would showup only minimally in storage benchmarks (which always use big, standalone servers).
Yes, but what about virtualization?
However real world, virtualized servers is another matter. I believe that virtualized servers generally demand more intensive I/O activity anyway and as one creates 5-10 VMs, ESX server, it’s almost guaranteed to have 5-10X the I/O happening. If each standalone VM requires 2-5% of a standalone processor to perform Open-FCoE processing, then it could easily represent 5-7 X 2-5% on a 10VM ESX server (assumes some optimization for virtualization, if virtualization degrades driver processing, it could be much worse), which would represent a serious burden.
Now these numbers are just guesses on my part but there is some price to pay for using host server MIPs for every FCoE frame and it does multiply for use with virtualized servers, that much I can guarantee you.
But the (storage) world is better now
Nonetheless, I must applaud Intel’s Open-FCoE thrust as it can open up a whole new potential market space that today’s CNAs maybe couldn’t touch. If it does that, it introduces low-end systems to the advantages of FCoE then as they grow moving their environments to real CNAs should be a relatively painless transition. And this is where the real advantage lies, getting smaller data centers on the right path early in life will make any subsequent adoption of hardware accelerated capabilities much easier.
But is it really open?
One problem I am having with the Intel announcement is the lack of other NIC vendors jumping in. In my mind, it can’t really be “open” until any 10GBE NIC can support it.
Which brings us back to Open-FCoE.org. I checked their website and could see no listing for a Windows driver and there was no NIC compatibility list. So, I am guessing their work has nothing to do with Intel’s driver, at least as presently defined – too bad
However, when Open-FCoE is really supported by any 10GB NIC, then the economies of scale can take off and it could really represent a low-end cost point for storage infrastructure.
Unclear to me what Intel has special in their x520 NIC to support Open-FCoE (maybe some TOE H/W with other special sauce) but anything special needs to be defined and standardized to allow broader adoption by other Vendors. Then and only then will Open-FCoE reach it’s full potential.
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So great for Intel, but it could be even better if a standardized definition of an “Open-FCoE NIC” were available, so other NIC manufacturers could readily adopt it.
InPhase Technologies Drive & Media (c) 2010 InPhase Technologies, All Rights Reserved (From their website)
Although InPhase Technologies and a few other startups had taken a shot at holographic storage over time, there has not been any recent innovation here that I can see.
Ecosystems matter
The real problem (which InPhase was trying to address) is to build up an ecosystem around their technology. In magnetic disk storage, you have media companies, head companies, and interface companies; in optical disk (Blu-Ray, DVDs, CDs) you have drive vendors, media vendors, and laser electronic providers; in magnetic tape, you have drive vendors, tape head vendors, and tape media vendors, etc. All of these corporate ecosystems are driving their respective technologies with joint and separate R&D funding, as fast as they can and gaining economies of scale from specialization.
Any holographic storage or any new storage technology for that matter would have to enter into the data storage market with a competitive product but the real trick is maintaining that competitiveness over time. That’s where an ecosystem and all their specialized R&D funding can help.
Market equavalence is fine, but technology trend parity is key
So let’s say holographic storage enters the market with a 260GB disk platter to compete against something like Blu-ray. Well today Blu-ray technology supports 26GB of data storage in single layer media, costing about $5 each and a drive costs about ~$60-$190. So to match todays Blu-ray capabilities holographic media would need to cost ~$50 and the holographic drive about ~$600-$1900. But that’s just today, dual layer Blu-Ray is available coming on line soon and in the labs, a 16-layer Blu-ray recording was demonstrated in 2008. To keep up with Blu-ray, holographic storage would need to demonstrate in their lab more than 4TB of data on a platter and be able to maintain similar cost multipliers for their media and drives. Hard to do with limited R&D funding.
As such, I believe it’s not enough to achieve parity to other technologies currently available, any new storage technology really has to be at least (in my estimation) 10x better in costs and performance right at the start in order to gain some sort of foothold that can be sustained. To do this against Blu-ray, optical holographic would need to start at 260GB platter for $5 with a drive at $60-$190 – just not there yet.
But NAND Flash/SSDs did it!
Yes, but the secret with NAND/SSDs was that they emerged from e-prom’s a small but lucrative market and later their technology was used in consumer products as a lower cost alternative/lower power/more rugged solution to extremely small form factor disk devices that were just starting to come online. We don’t hear about extremely small factor disk drives anymore because NAND flash won out. Once NAND flash held the market there, consumer product volumes were able to drive costs down and entice the creation of a valuable multi-company/multi-continent ecosystem. From there, it was only a matter of time before NAND technologies became dense and cheap enough to be used in SSDs addressing the more interesting and potential more lucrative enterprise data storage domain.
So how can optical holographic storage do it?
Maybe the real problem for holographic storage was its aim at the enterprise data storage market, perhaps if they could have gone after some specialized or consumer market and carved out a niche, they could have created an ecosystem. Media and Entertainment has some pretty serious data storage requirements which might be a good match. InPhase was making some inroads there but couldn’t seem to put it altogether.
So what’s left for holographic technology to go after – perhaps medical imaging. It would play to holographic’s storage strengths (ability to densely record multiple photographs). It’s very niche-like with a few medical instrument players developing MRI, cat scans and other imaging technology that all require lot’s of data storage and long-term retention is a definite plus. Perhaps, if holographic technology could collaborate with a medical instrument consortium to establish a beachhead and develop some sort of multi-company ecosystem, it could move out from there. Of course, magnetic disk and tape are also going after this market, so this isn’t a certainty but there may be others markets like this out there, e.g., check imaging, satellite imagery, etc. Something specialized like this could be just the place to hunker down, build an ecosystem and in 5-7 years, emerge to attack general data storage again.
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 Backup, Gladinet, Nasuni, 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.
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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…
