Re: Linux 2.6.29

Linus Torvalds
2009-03-25T18:34:20Z

On Wed, 25 Mar 2009, Linus Torvalds wrote:
>
> Even a suck-ass laptop drive can write streaming data fast enough that
> people don't care. The problem is invariably that writes from different
> sources (much of it being metadata) interact and cause seeking.

Actually, not just writes.

The IO priority thing is almost certainly that _reads_ (which get higher
priority by default due to being synchronous) get interspersed with the
writes, and then even if you _could_ be having streaming writes, what you
actually end up with is lots of seeking.

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.

Linus