On Mon, Dec 9, 2013 at 12:30 PM, Jim Klimov <[email protected]> wrote:
> On 2013-12-09 19:57, Saso Kiselkov wrote: > >> Right, but how could this result in >2x the performance? As indicated >>> by your diagram, you are doing at most 2 reads at once (or, you are >>> getting at most 1 read "for free" while the CPU is busy processing the >>> last block). You claimed a 10-20x speedup (I am assuming that "several" >>> means 3). >>> >> >> As I said, I'm gonna have to recheck, it's possible I might be >> remembering stuff incorrectly. However, currently my possibilities for >> performance testing are somewhat limited. I'll get back to you as soon >> as I have more info. >> > > Speaking from the theoretical peanut gallery, the SSDs' modern > speediness is due to their amount of NAND chips, each doing some > 20MB/s or so (figures non-authoritative). So if multiple queued > tasks land on different chips - and there are dozens of them now - > it may indeed be much faster than single-chip single-requests. > The device can indeed issue operations to the chips in parallel > and return answers as they come into its buffers. Maybe so... > > Yes, if we issue N concurrent i/os, it could be up to N times faster than if we issue one i/o. In this case, N=2. --matt
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