Re: Performance of a software raid 5

[Corey Hickey <bugfood-ml@fatooh.org>]

Johannes Segitz 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

If it helps, some recent dd benchmarks I did indicate that twofish is
about 25% faster than aes on my Athlon64.

Athlon64 3400+ 2.4 GHz, 64-bit Linux 2.6.28.2

Both aes and twofish are using the asm implementations according to
/proc/crypto.

All numbers are in MB/s; average of three tests for a 512MB dd
read/write to the encrypted device.

                                 read       write
aes                              69.4        61.0
twofish                          86.8        76.6
aes-cbc-essiv:sha256             65.1        56.3
twofish-cbc-essiv:sha256         82.6        73.5


-Corey