Dana H. Myers wrote:
Jonathan Wheeler wrote:
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
mirror MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
8 disk 8196 33285 38.6 46033 9.9 33077 6.8 67934 90.4 93445 7.7 230.5 1.3
8 disk 8196 34821 41.4 46136 9.0 32445 6.6 67120 89.1 94403 6.9 210.4 1.8
46MB/sec writes, each disk individually can do better, but I guess keeping 8
disks in sync is hurting performance. The 94MB/sec writes is interesting. One
the one hand, that's greater then 1 disk's worth, so I'm getting striping
performance out of a mirror GO ZFS. On the other, if I can get striping
performance from mirrored reads, why is it only 94MB/sec? Seemingly it's not
cpu bound.
I expect a mirror to perform about the same as a single disk for writes, and
about
the same as two disks for reads, which seems to be the case here. Someone from
the ZFS team can correct me, but I tend to believe that reads from a mirror are
scheduled in pairs; it doesn't help the read performance to have 6 more copies
of
the same data available.
Is this an 8-way mirror, or a 4x2 RAID-1+0? For the former, I agree with Dana.
For the latter, you should get more available space and better performance.
8-way mirror:
zpool create blah mirror c1d0 c1d1 c1d2 c1d3 c1d4 c1d5 c1d6 c1d7
4x2-way mirror:
zpool create blag mirror c1d0 c1d1 mirror c1d2 c1d3 mirror c1d4 c1d5
mirror c1d6 c1d7
-- richard
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