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Compared to other offerings currently on the market, the system comes in at a higher capacity (the next-biggest all-Flash system is Texas Memory Systems’ 5 TB RAM-SAN 620) and cheaper (TMS’s system costs $220,000). However, there’s one catch: WhipTail uses multi-level cell (MLC) drives instead of single-level cell (SLC) drives.
Most enterprise solid state drive offerings are based on SLC drives, which have one physical layer on which data is recorded. MLC drives are cheaper, more common in consumer devices, and can hold more data. However, their reliability is generally considered lower than SLC drives because of the complexity of writes to multiple physical layers, cheaper raw materials in some cases, and fewer lifetime write cycles supported.
This is where WhipTail’s software IP comes in, according to CEO Edward Rebholz. The software buffers writes to the system using DRAM and splits the writes to NAND capacity into 2-bit blocks to match the size of each cell on the back-end MLC SSDs, which cuts down on wear to the Flash drives and so prolongs their life cycle.
WhipTail also works with MLC drive suppliers using an “extensive quality control process internally”, Rebholz said. According to the CEO, MLC has also gotten much of its unreliable rep from previous generations of drives made up of 3-bit and 4-bit cells. “Two-bit drives are much better,” Rebholz says. All of this adds up to internal WhipTail estimates that it can make an MLC drive last for about seven years with a full overwrite per day. “On average companies overwrite about 25% every day,” Rebholz pointed out.
With a company so new, that lifespan for MLC drives obviously hasn’t been proven out in the market yet. Storage admins have expressed a desire to see larger SSDs, although that usually means capacity and cost per gigabyte of individual drives rather than pools. They might be intrigued by a lower cost per gigabyte (WhipTail also sells 1.5 TB and 3 TB systems for around $46,000 and $75,600 respectively), although capital expenditures on new technologies are among the most difficult projects to get funded in the current economy.
Another alternative is the single mode level cell (SMLC) drives that Fusion-io launched this week.
For some applications, SSD can be a more efficient alternative both in terms of capex and energy costs to short-stroking conventional hard disk drives. Users going this route may find the price points WhipTail’s offering in a recession more attractive than SLC-based products, but there’s still the matter of trusting the software to provide reliability. I will be curious which direction users will choose to go.