raidz2 a bit big

[Artis Caune]

2009/5/26  <peterjeremy at optushome.com.au>:
> On 2009-May-23 15:37:14 +0300, Artis Caune <artis.caune at gmail.com> wrote:
>>2009/5/23 Randy Bush <randy at psg.com>:
>>> a dozen 2tb drives in a raidz2
>>Reads on such configurations are very slow.
>
> Not really.  Assuming each disk is capable of X IOPS and assuming
> non-degraded mode, you can still issue (N-2)*X random reads/sec
> because the parity stripes are not needed/used.  (Compared to N*X
> random reads/sec for a mirrored configuration).  Degraded reads _are_
> very slow because you need to read most of the spindles (I'm not sure
> of the exact recovery mechanism for RAIDZ2 but it's probably close to
> X random reads/sec).


Not really,

RAID{5,6} != RAIDZ{1,2}

http://blogs.sun.com/roch/entry/when_to_and_not_to
http://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSRaidzReadPerformance

We switched 20K mailboxes from raidz2 to mirror because of slow reads.





-- 
Artis Caune

    Everything should be made as simple as possible, but not simpler.