On Fri, Jul 20, 2007 at 09:58:50AM -0400, Justin Piszcz wrote:
> I have a multi-core Q6600 CPU on a 10-disk Raptor RAID 5 running XFS.
>
> I just pulled down the Debian Etch 4.0 DVD ISO's, one for x86 and one for
> x86_64, when I ran md5sum -c MD5SUMS, I see ~280-320MB/s. When I ran the
> second one I see upwards of what I should be seeing 500-520MB/s.
>
> NOTE:: These MD5 contain the 3 DVD ISO's for each platform, 6 total ISOs.
>
> I know md5sum is cpubound to a degree, do you think that is what is
> happening here? Each core can only sustain ~300MB/s and then with two of
> four cores working, it can exceed that amount or is there some similarity
> with RAID1 in linux compared to RAID5?
>
> With RAID1, if you use a single read thread, you will get 60-70MB/s read
> on a dual raptor raid1. If you use two(?) or three threads, it will read
> from both disks and you will see 120-140MB/s.
>
> Is there some commonality with software RAID1 and RAID5 in Linux in this
> regard?
Could you just run top while doing md5sum and see how much cpu md5sum is
using on the cpu it is on? After all if it says 100% for the process,
then yes it is cpu bound at 300MB/s, and if not then I guess there has
to be another explanation.
It looks pretty likely, since I just tried running md5sum on a 130MB
file here, and it takes 0.444s of user cpu time and 0.068s of system
time to process, and I ran it multiple times so the file ended up cached
in ram so disk speed isn't a concern, which I figure means my system
runs md5sum at about 250MB/s. This is on a single core Athlon 64 3500+
(2.2GHz). So if you have a slightly faster as you do with a 2.4GHz Core
2, then 300MB/s seems perfectly reasonable per core. I don't quite know
how md5 hashes work, but I really doubt they are something you are
likely to be able to make threaded.
--
Len Sorensen
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