Linux Software RAID5 Performance

Jurgen Botz jurgen at botz.org
Wed Apr 3 13:25:31 EST 2002


Michael Prinkey wrote:
> Again, performance (see below) is remarkably good, especially considering 
> all of the strikes against this configuration:  EIDE instead of SCSI, UDMA66 
> instead of 100/133, 5400-RPM instead of 7200-RPM, and master/slave drives on 
> each port instead of a single drive per port. 

With regard to the master/slave config... I note that your performance
test is a single reader/writer... in this config with RAID5 I would
expect the performance to be quite good even with 2 drives per IDE
controller.  But if you have several processes doing disk I/O
simultaneously you should see a rather more precipitous drop in
performance than you would with a single drive per IDE controller.
I'm working on testing a very similar config right now and that's 
one of my findings (which I had expected) but our application for this
is not very performance sensitive so it's not a big deal.

A more important issue for me is reliability, and I'm somewhat 
concerned about failure modes.  For example, can an IDE drive fail
in such a way that if will disable the controller or the other
drive on the same controller?  If so, that would seriously limit
the usefulness of RAID5 in this config.  In general how good is
Linux software RAID's failure handling?  Etc.

:j


-- 
Jürgen Botz                       | While differing widely in the various
jurgen at botz.org                   | little bits we know, in our infinite
                                  | ignorance we are all equal. -Karl Popper


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