TMS doubles flash RamSan Fibre Channel speed
Working on eMLC flash RamSan
TMS has doubled its flash-based RamSan-630's Fibre Channel speed from 4 to 8Gbit/s, meaning 10GB/sec bandwidth, and is working on eMLC-based flash product.
The 630 is a 3U enclosure holding up to 10TB of single level cell (SLC) flash with up to 10 Infiniband (IB) or Fibre Channel ports. It delivers 10GB/sec across the IB ports but had achieved only 4GB/sec across a Fibre Channel fabric. Now the FC side of things has speeded up to 8GB/sec. TMS says that means applications relying on high Fibre Channel bandwidth from SAN arrays can now think about replacing them with a faster-responding RamSan-630.
The 630 can run at 1 million IOPS (random reads of 4KB data blocks) over IB and 800,000 over 8gig FC, 400,000 over 4gig FC. TMS designs and builds its own interface chip sets to get to these speed levels and has done so since the original RamSan-210, which supported 1gig FC. The 1gig FC host bus adapters then available from suppliers including QLogic and Emulex were not fast enough for TMS' needs.
Enterprise-grade MLC flash
Jamon Bowen, TMS's director for sales engineering, said TMS was looking closely at multi-level cell (MLC) flash, as this is cheaper than the SLC NAND used in the 630. For comparison's sake he said SLC flash can do 100,000 write/erase cycles and MLC 10,000. The next shrink of MLC will do just 3,000 write/erase cycles, as a consequence of the process geometry down-sizing. Bowen said: "I don't think that's usable by our customer base," – and, no, he wasn't speaking with his tongue in his cheek.
Fortunately, there is enterprise-grade MLC (eMLC) from suppliers such as Micron, which will do 30,000 write/erase cycles. It has different circuitry which, Bowen says, holds high voltage levels for different times at floating gates compared to ordinary MLC. The resulting eMLC chips are still cheaper than SLC.
However the write and erase times are longer than both SLC and MLC flash. This matters for consumer apps but less so for the read-intensive enterprise apps, such as data warehousing, TMS RamSans support. Bowen says smart controller design can write data to empty cells avoiding the real-time erase penalty with background garbage (deleted cell) collection and erasure.
Over-provisioning also helps to ensure that any eMLC product has an adequate working life. There is no word on when an eMLC RamSan might appear.
Kaminario critique 'completely off'
TMS also supplies RAM-based products, branded the RamSan-300, -400 and -440. Competitor Kaminario, which supplies DRAM SSDs via ganging together Dell servers in a grid, says the TMS approach is flawed.
It says that the RamSan is a single box, contrasting with Kaminario's scale-out design which enables incremental growth. Customers need a separate RamSan box to protect against failure whereas the Kaminario grid has an N+1 design, meaning failover is built-in. Kaminario also claims: "The flash part of their product has poor utilisation of capacity and degrades over time; we offer consistent performance no matter what the workload. We offer 100 per cent media utilisation."
Bowen said: "[Firstly] our systems are distributed 2-4u systems that can be upgraded internally and additional systems and additional units can easily be added scale capacity."
Concerning the failure issue: "For no-single-point-of-failure configurations we deploy mirrored units in the same fashion that [Kaminario] markets. The difference is where the mirroring is. They have an appliance that receives the I/O and then propagates it to two of their data units which we mirror from the host. The mirroring from the host eliminates the propagation delay of an additional appliance and lowers the latency (which is critical for SSDs.) It also allows us to mix with traditional storage in a preferred read configuration where reads come exclusively from us and writes go to both."
He gave short shrift to the Kaminario point about TMS flash having poor-capacity utilisation: "The argument that flash offers poor capacity compared to RAM is completely off. Flash requires management and hardware engineering prowess, but offers massively more capacity than RAM at a similar price point. This is the reason that TMS embraced flash in 2006... For high-capacity SSD deployments, flash is what our customers look at."
We hear that the RAM SSD external storage device market is not growing much. Flash is where the growth is in the external accelerated storage device market. With TMS historically building and integrating RamSan components itself – apart from the DRAM and NAND chips – it reckons it has a bandwidth performance advantage compared to other suppliers using commodity components as well as commodity base chips. We might expect, then, that any coming eMLC TMS array will be faster than equivalent ones from suppliers such as Violin Memory.
The 8Gbit/s FC-381 adapter for the RamSan-630 is available now. Self-service price quotes are available at www.ramsan.com/FC. ®
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