Re: Linux 2.6.29

Alan Cox
2009-03-25T18:50:57Z

> Again, good SSD's don't care. Disks do. It doesn't matter if you have a FC
> disk array that can eat 300MB/s when streaming - once you start seeking,
> that 300MB/s goes down like a rock. Battery-protected write caches will
> help - but not a whole lot when streaming more data than they have RAM.
> Basic queuing theory.

Subtly more complex than that. If your mashed up I/O streams fit into the
2GB or so of cache (minus one stream to disk) you win. You also win
because you take a lot of fragmented OS I/O and turn it into bigger
chunks of writing better scheduled. The latter win arguably shouldn't
happen but it does occur (I guess in part that says we suck) and it
occurs big time when you've got multiple accessors to a shared storage
system (where the host OS's can't help)

Alan