XcelaSAN is a caching appliance that sits between a Fibre Channel (FC) switch and storage array. XcelaSAN automatically brings the most frequently used blocks of data in an FC SAN into DRAM and then NAND to speed performance. It works with any vendor's FC SAN, according to Dataram chief technologist Jason Caulkins. Unlike disk array-based solid-state drives (SSDs), the XcelaSAN isn't intended to be persistent storage. The appliance moves data to back-end hard disk drives.
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The product is the first NAND product the memory controller maker has rolled out, although Caulkins said the 42-year-old company designed a kind of proto-SSD with a disk drive interface in 1976.
XcelaSAN is the result of that acquisition, combining Cenatek's standalone direct-attach SSD IP with Dataram's memory controllers and DRAM into a 2U network device. The product holds 128 GB of RAM cache and 360 GB of Flash, and can be clustered into high-availability pairs and stacked for capacity scaling. Each appliance costs $65,000. Dataram claims the device can perform at 450,000 IOPS or 3 GBps throughput.
It's similar in architecture to Gear6's NFS read caching device, but supports block storage and write caching as well. Another similar product is NetApp Inc.'s FlexCache, which is also focused on NFS and NetApp storage, although it can theoretically be combined with NetApp's V-Series storage virtualization gateway to front heterogeneous storage.
Caulkins argued that Dataram's block-based approach, combined with a caching appliance rather than array-based SSDs, is the most efficient use of Flash. EMC Corp. and others argue that the presence of an SSD makes the entire network loop between server and storage array faster, while Fusion-io Inc. takes another tack claiming Flash make the most sense as close to the server bus as possible.
"It's not cost-effective to put all of your data on SSDs," Caulkins said. "It's better to be able to immediately impact performance without changing files, moving data or figuring out what to put on the SSD."
Analysts debate user interest in XcelaSANAndrew Reichman, a senior analyst at Cambridge, Mass.-based Forrester Research Inc., said it makes sense to use XcelaSAN's solid-state drive as cache rather than persistent storage. "It's more effective to only move blocks that are being frequently requested than to move whole volumes to solid-state storage," he said.
Reichman said the Dataram device is pricey, especially as solid-state vendors, including Fusion-io, STEC Inc. and WhipTail Technologies, have begun using less expensive multi-level cell (MLC) Flash combined with RAID data protection schemes to make enterprise-class devices more affordable.
However, Reichman pointed out that Dataram may find interest among organizations seeking performance over price. "The high end of the market is who's going to care about performance the most and have the budget for it," he said. "A company that really cares about performance and is willing to spend more money for it may compare this to short-stroking disks and find it cost-effective."
Of course, XcelaSAN has yet to be tested in the marketplace. Dataram claims beta users but has no public customer references at this time. "From a theoretical perspective it makes sense," Reichman said. "But I can't speak to how effective it actually is."
Mark Peters, an analyst at Milford, Mass.-based Enterprise Strategy Group, said some organizations find Flash-as-disk effective despite the theoretical limitations cited by Reichman. "I think if you know what your problem data is and you can put it on solid state, that's absolutely wonderful," he said. "If not, or if that data changes every day, a caching device might be more appropriate."
That said, while Dataram has been in the memory business for quite some time, they aren't well-known in the storage market, Peters pointed out. "Distribution is usually the biggest challenge in this business," he said."