ZFS Hangs

Peter Schuller 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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