Ian Collins wrote:
Bart Smaalders wrote:
michael T sedwick wrote:
Given a 1.6TB ZFS Z-Raid consisting 6 disks:
And a system that does an extreme amount of small /(<20K) /random
reads /(more than twice as many reads as writes) /
1) What performance gains, if any does Z-Raid offer over other RAID
or Large filesystem configurations?
2) What is any hindrance is Z-Raid to this configuration, given the
complete randomness and size of these accesses?
Would there be a better means of configuring a ZFS environment for
this type of activity?
thanks;
A 6 disk raidz set is not optimal for random reads, since each disk in
the raidz set needs to be accessed to retrieve each item. Note that if
the reads are single threaded, this doesn't apply. However, if multiple
reads are extant at the same time, configuring the disks as 2 sets of
3 disk raidz vdevs or 3 pairs of mirrored disk will result in 2x and 3x
(approx) total parallel random read throughput.
I'm not sure why, but when I was testing various configurations with
bonnie++, 3 pairs of mirrors did give about 3x the random read
performance of a 6 disk raidz, but with 4 pairs, the random read
performance dropped by 50%:
3x2
Block read: 220464
Random read: 1520.1
4x2
Block read: 295747
Random read: 765.3
Ian
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interesting.... I wonder if the blocks being read were stripped across
two mirror pairs; this would result in having to read 2 sets
of mirror pairs, which would produce the reported results...
- Bart
--
Bart Smaalders Solaris Kernel Performance
[EMAIL PROTECTED] http://blogs.sun.com/barts
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