On 27 November 2010 08:05, Krunal Desai <mov...@gmail.com> wrote: > One new thought occurred to me; I know some of the 4K drives emulate 512 > byte sectors, so to the host OS, they appear to be no different than other > 512b drives. With this additional layer of emulation, I would assume that > ashift wouldn't be needed, though I have read reports of this affecting > performance. I think I'll need to confirm what drives do what exactly and > then decide on an ashift if needed. >
If you consider that for a 4KB internal drive, with a 512B external interface, a request for a 512B write will result in the drive reading 4KB, modifying it (putting the new 512B in) and then writing the 4KB out again. This is terrible from a latency perspective. I recall seeing 20 IOPS on a WD EARS 2TB drive (ie, 50ms latency for random 512B writes).
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