peter.schuller at infidyne.com
Sun Nov 4 09:18:24 PST 2007
> Well the readahead "issues" are just the zfs design, AFAIK. It does
> aggressive prefetching to improve performance on the assumption that you
> are running with a reasonably fast storage system that can keep up. On
> crappy low end disk hardware (e.g. single ATA disk) this can easily
> saturate the disk.
Well, regardless of the absolute performance you don't want the read-ahead to
consume to much of the relative bandwidth/seek time available.
Personally I didn't experience any prooven issues with prefetch; I disabled it
on general recommendation back in the i386/1gb days and told myself I saw an
improvement. I never looked into it carefully, other than that I previously
had a general feeling that I saw a lot more I/O on the pool than what was
read by applications. My memories are vague.
/ Peter Schuller
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