SuperTalent adds Ram to SSD to boost write speeds
Eight-channel Flash architecture helps too
SuperTalent has begun shipping SSDs with 128MB of on-board DRam in a bid to beat the poor random write performance of so many solid-state drives.
The 2.5in MasterDrive SX line includes capacities of 64GB, 128GB and 256GB. The latter have the same read and write speeds of 220MB/s and 200MB/s, respectively, SuperTalent said. For the lower-capacity unit, those speeds fall to 200MB/s and 120MB/s, respectively.
All three drives connect over 3Gb/s Sata. They're based on multi-layer cell (MLC) Flash, not the fastest form of the non-volatile memory, but SuperTalent said it was using an eight-channel architecture with an "advanced new eight-channel controller".
All that Ram is used to cache random writes which can then be combined to mask slow MLC random writes and take advantage of the Flash chips' higher sequential write speeds. Just so long as the power doesn't go before the cache contents have been written out.
ST didn't put a price to the 256GB drive, but online prices put the 64GB model around the $175 (£107/€126) mark and the 128GB version at $359 (£219/€258). ®
You can indeed put non-volatile write cache into an array (well, technically speaking, battery backed up cache and, if the manufacturer is wise, either a buffer-write out to disk or full destage under batter power for long term power outages - as they found to their costs in Canada a few years back when mains power was lost for many days after an ice storm).
However, the array based approach is hardly cost effective for individual PCs. Even in the case of arrays, then there is a good reason for going this way. If each device has its own NV write cache allowing for full buffer destage (either powered from an internal battery/capacitor, or by a battery in the array), then a hhuge amount of cost could be removed from the array. All the arrays I know are configured with RAID protection. In that case, even if one SSD fails, then the data is still available. It then means that all that expensive mirrored and battery backed up write cache in the array can be junked as the low latency of writes to these new devices means that these can all be synchronous. There might still be a need for some of this mirrored memory - the array will have all sorts of state information to maintain, and you wouldn't want a storage system crash in the event of the failure of a critical component. However, even then it might be possible to do without it. SUN's unified storage appliance does not have an NV mirrored write cache. It has the option for write-optimised SSD for this purpose (in a resilient configuration), although node failure results in a disruptive failover as state information is not mirrored across and ZFS is not a clustered file system. However, that could be dealt with in the future.
If open storage platforms are to take off, then expensive, proprietary hardware like mirrored NR RAM probably need to go too.
Cache needs to be mirrored and battery backed. Manufacturers figured out a long time ago that this is best done at the array controller level rather than on individual disks.
Not necessarily blah!
They just need a BFC (big friggin capacitor) to hold enough charge to last through a full write cycle after power is cut. And since we're talking pure solid state, it probably doesn't need that much current in the first place.
Where to buy?
Anyone seen a UK retailer/e-tailer?
Provided that they have designed in some short term power storage (a super capacitor or small battery?) to allow the data from the ram to be destaged to flash then it should be fine. There is surely space in a standard hard disk form factor for such a thing - it only needs to supply the device and as they are only a couple of watts then providing a few seconds of power is surely possible.
Roll-up write optimisation like this is an obvious way to deal with the poor random write performance of flash, and it should also help with keeping the number of write cycles down to extend the life of the device. Of course roll-up optimisation is likely to cause fragementation, but with random access time so low it hardly matters that much.
I might try one of these out as a system disk which is what gets hammered on my PC.