Re: Performance of a software raid 5

[Johannes Segitz <johannes.segitz@gmail.com>]

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

Johannes
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