SANDISK HAS UPPED the ante on their newest generation of SSDs, not just faster, but also smarter. Some of this is also trickling down to their lines of netbook SSDs as well.
Most SSDs are just a controller and some flash, both off the shelf products. To get real performance, you need to do your own thing, which usually means designing a controller and a lot of engineering. Many companies don’t bother with this step, but Sandisk is one of the few that takes the engineering to the proverbial next level with the new G3 drives.
More than just flash in a box
The idea is simple, add a cache in and tune the file system to the strengths of flash memory rather than the strengths of magnetic media. Since most flash chips are block based devices, they fall over on small writes and updates. This is where the file system comes in.
If you write to a flash device, it has to write a whole block. A single byte written forces a 4K (usually, depends on the device) block to be written. Worse yet, you often have to read in the block you are writing to, modify it with the new data, and then write the full block back. This, and a lot of other technical minutia makes things go very very slowly when doing multiple small writes.
The solution to this is what Sandisk calls Extreme FFS, basically a file system that understands flash well. The exact algorithms it uses is proprietary, but the general concept, to queue up small files and only write when you have a full block of data is easy enough to understand.
Not only does this minimize inefficient individual writes, but it also minimizes the number of blocks written in total, so the SSD does not wear out as fast. Partially written blocks also lead to a lot of unused space, and unused space needs to be compacted and reclaimed. Extreme FFS minimizes garbage collection by minimizing partially used blocks, something that most people mistake for fragmentation. It is a win/win.
All of this works in concert with a cache SLC flash. It speeds things up noticeably by allowing the file system to have a lot of flexibility in doing the low level twiddling that makes drives fast. On the netbook SSDs, the cache is about 700MB for every 32G of SSD space. G3 SSDs will be on the market in Q3, and as always, price will be determined by flash costs more than anything else.
Caseless upgrades
Speaking of SSDs for netbooks, Sandisk has the pSSD line for that market. Given the state of netbooks a year or so ago, the p used to stand for PATA. Now, with netbooks blossoming into crotchtops, netbooks, actual useful devices, and other things, PATA in the segment has gone the way of PATA everywhere else.
Now, the p in pSSD stands for pico, and that they are. For cost reasons, Sandisk doesn’t put in all the goodies of the G3 line, it would get too expensive, but they do have some caching, and now have capacities up to 64GB. The rest of the goodies will trickle down to netbook level drives as prices warrant, but for now, the second gen pSSD drives should be fairly speedy.S|A
Charlie Demerjian
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