We were talking with Pure Storage last week, another SSD startup which just emerged out of stealth mode today. Somewhat like SolidFire which we discussed a month or so ago, Pure Storage uses only SSDs to provide primary storage. In this case, they are supporting a FC front end, with an all SSDs backend, and implementing internal data deduplication and compression, to try to address the needs of enterprise tier 1 storage.
Pure Storage is in final beta testing with their product and plan to GA sometime around the end of the year.
Pure Storage hardware
Their system is built around MLC SSDs which are available from many vendors but with a strategic investment from Samsung, currently use that vendor’s storage. As we know, MLC has write endurance limitations but Pure Storage was built from the ground up knowing they were going to use this technology and have built their IP to counteract these issues.
The system is available in one or two controller configurations, with an Infiniband interconnect between the controllers, 6Gbps SAS backend, 48GB of DRAM per controller for caching purposes, and NV-RAM for power outages. Each controller has 12-cores supplied by 2-Intel Xeon processor chips.
With the first release they are limiting the controllers to one or two (HA option) but their storage system is capable of clustering together many more, maybe even up to 8-controllers using the Infiniband back end.
Each storage shelf provides 5.5TB of raw storage using 2.5″ 256GB MLC SSDs. It looks like each controller can handle up to 2-storage shelfs with the HA (dual controller option) supporting 4 drive shelfs for up to 22TB of raw storage.
Pure Storage Performance
Although these numbers are not independently verified, the company says a single controller (with 1-storage shelf) they can do 200K sustained 4K random read IOPS, 2GB/sec bandwidth, 140K sustained write IOPS, or 500MB/s of write bandwidth. A dual controller system (with 2-storage shelfs) can achieve 300K random read IOPS, 3GB/sec bandwidth, 180K write IOPS or 1GB/sec of write bandwidth. They also claim that they can do all this IO with an under 1 msec. latency.
One of the things they pride themselves on is consistent performance. They have built their storage such that they can deliver this consistent performance even under load conditions.
Given the amount of SSDs in their system this isn’t screaming performance but is certainly up there with many enterprise class systems sporting over 1000 disks. The random write performance is not bad considering this is MLC. On the other hand the sequential write bandwidth is probably their weakest spec and reflects their use of MLC flash.
Purity software
One key to Pure Storage (and SolidFire for that matter) is their use of inline data compression and deduplication. By using these techniques and basing their system storage on MLC, Pure Storage believes they can close the price gap between disk and SSD storage systems.
The problems with data reduction technologies is that not all environments can benefit from them and they both require lots of CPU power to perform well. Pure Storage believes they have the horsepower (with 12 cores per controller) to support these services and are focusing their sales activities on those (VMware, Oracle, and SQL server) environments which have historically proven to be good candidates for data reduction.
In addition, they perform a lot of optimizations in their backend data layout to prolong the life of MLC storage. Specifically, they use a write chunk size that matches the underlying MLC SSDs page width so as not to waste endurance with partial data writes. Also they migrate old data to new locations occasionally to maintain “data freshness” which can be a problem with MLC storage if the data is not touched often enough. Probably other stuff as well, but essentially they are tuning their backend use to optimize endurance and performance of their SSD storage.
Furthermore, they have created a new RAID 3D scheme which provides an adaptive parity scheme based on the number of available drives that protects against any dual SSD failure. They provide triple parity, dual parity for drive failures and another parity for unrecoverable bit errors within a data payload. In most cases, a failed drive will not induce an immediate rebuild but rather a reconfiguration of data and parity to accommodate the failing drive and rebuild it onto new drives over time.
At the moment, they don’t have snapshots or data replication but they said these capabilities are on their roadmap for future delivery.
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In the mean time, all SSD storage systems seem to be coming out of the wood work. We mentioned SolidFire, but WhipTail is another one and I am sure there are plenty more in stealth waiting for the right moment to emerge.
I was at a conference about two months ago where I predicted that all SSD systems would be coming out with little of the engineering development of storage systems of yore. Based on the performance available from a single SSD, one wouldn’t need 100s of SSDs to generate 100K IOPS or more. Pure Storage is doing this level of IO with only 22 MLC SSDs and a high-end, but essentially off-the-shelf controller.
Just imagine what one could do if you threw some custom hardware at it…
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