Re: Performance of a software raid 5

[Neil Brown <neilb@suse.de>]

On Tuesday April 21, johannes.segitz@gmail.com wrote:
> On Tue, Apr 21, 2009 at 3:19 AM, NeilBrown <neilb@suse.de> wrote:
> > Have you done any testing without the crypto layer to see what effect
> > that has?
> >
> > Can I suggest:
> >
> >  for d in /dev/sd[gjk]1 /dev/md6 /dev/mapper/data bigfile
> >  do
> >    dd if=$d of=/dev/null bs=1M count=100
> >  done
> >
> > and report the times.
> 
> tested it with 1gb instead of 100 mb
> 
> sdg
> 1048576000 bytes (1.0 GB) copied, 9.89311 s, 106 MB/s
> sdj
> 1048576000 bytes (1.0 GB) copied, 10.094 s, 104 MB/s
> sdk
> 1048576000 bytes (1.0 GB) copied, 8.53513 s, 123 MB/s
> /dev/md6
> 1048576000 bytes (1.0 GB) copied, 11.4741 s, 91.4 MB/s
> /dev/mapper/data
> 1048576000 bytes (1.0 GB) copied, 34.4544 s, 30.4 MB/s
> bigfile
> 1048576000 bytes (1.0 GB) copied, 26.6532 s, 39.3 MB/s
> 
> so the crypto indeed slows it down (and i'm surprised that it's that
> bad because i've read
> it's not a big hit on current CPUs and the X2 isn't new but not that
> old) but still read speed
> from md6 is worse than from one drive alone

I suspect you will see that improve when you add another drive that it
isn't running degraded.

NeilBrown
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