There is a common misconception about the comparison between
mirror and raidz.
You get the same performance, when you use the same number of disks.
But the resulting filesystem has a different sizre, therefore a comparison
is not applicable.
Example: you have 8 disks
Compare a zpool with one raidz vdev with 8 disks
with a zpool containing 4 mirrors of 2 disks each.
Then the read IOs spread over 8 disks in each case.
Therfore the number of IOs is comparable
But you compared apples and oranges because the net size
is 7 disks in the first case and 4 disks in the second case.
A valid comparison would be a comparison of a zpool with
one raidz vdev containing 5 disks with the mirrored zpool
containing 4 mirrors of 2 disks each.
Because then the size of the zpool is the same.
Regards,
Ulrich
Roy Sigurd Karlsbakk wrote:
----- Original Message -----
On Jul 20, 2010, at 6:12 AM, v <victor_zh...@hotmail.com> wrote:
Hi,
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.
On reads, no, any part of the stripe width can be read without reading
the whole stripe width, giving performance equal to raid0 of
non-parity disks.
Are you sure this is true? I know it is, in theory, but some testing with
bonnie++ showed me I didn't get so large a gain. Perhaps my tests were done
wrong?
Vennlige hilsener / Best regards
roy
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