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Re: [Xen-users] Software Raid 5 domu performance drop

> On 5/26/2013 8:39 AM, Micky wrote:
> > Software raids by design have huge performance hits. I won't really
> > use dmraid in production.
> Raid 5 also has significantly more more I/O delays & performance hits
> since a single Write usually causes two Reads, then processing, finally
> two Writes. It gets even worse when sync'ing or if something waits for
> the the operation to complete before continuing.
> Anyone using S/W raid (and sometimes even with h/w raid) is better off
> using Raid 1 or Raid 10 if you are concerned with performance.

According to a recent post - 
http://comments.gmane.org/gmane.linux.kernel.bcache.devel/1713 - bcache now has 
some smarts for raid5 where it tries to write out an entire stripe where 
possible. If you have a fast flash disk and can compile your own kernel then 
bcache is the only way I would recommend using software raid5 where performance 
matters. Also in theory it might close the raid5 write hole.


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