On 21/07/2010 15:40, Edward Ned Harvey wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of v
for zfs raidz1, I know for random io, iops of a raidz1 vdev eqaul to
one physical disk iops, since raidz1 is like raid5 , so is raid5 has
same performance like raidz1? ie. random iops equal to one physical
disk's ipos.
I tested this extensively about 6 months ago. Please see
http://www.nedharvey.com for more details. I disagree with the assumptions
you've made above, and I'll say this instead:
Look at
http://nedharvey.com/iozone_weezer/bobs%20method/iozone%20results%20summary.
pdf
Go down to the 2nd section, "Compared to a single disk"
Look at "single-disk" and "raidz-5disks" and "raid5-5disks-hardware"
You'll see that both raidz and raid5 are significantly faster than a single
disk in all types of operations. In all cases, raidz is approximately equal
to, or significantly faster than hardware raid5.
I had a quick look at your results a moment ago.
The problem is that you used a server with 4GB of RAM + a raid card with
a 256MB of cache.
Then your filesize for iozone was set to 4GB - so random or not you
probably had a relatively good cache hit ratio for random reads. And
even then a random read from 8 threads gave you only about 40% more IOPS
than for a RAID-Z made out of 5 disks than a single drive. The poor
result for HW-R5 is surprising though but it might be that a stripe size
was not matched to ZFS recordsize and iozone block size in this case.
The issue with raid-z and random reads is that as cache hit ratio goes
down to 0 the IOPS approaches IOPS of a single drive. For a little bit
more information see http://blogs.sun.com/roch/entry/when_to_and_not_to
--
Robert Milkowski
http://milek.blogspot.com
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