high load

high load

[Phil Garcia]

Hi,

We've come across a problem that seems related to the interaction
between NFS and a 3ware 7500-8 running RAID 5 with one hot spare.  We
have a test program that opens a file and then loops, writing up to
255 bytes to the file and then sleeping for up to 10 seconds.  We run
around 200 instances of the program simultaneously for about 25
minutes.

When we run the processes on 200 separate slaves, writing to a
(reiserfs) directory under the 3ware controller, the load on the
server shoots up to over 20 and then gradually declines over the next
5 minutes or so.

When we run the processes on 200 separate slaves, writing to a
different disk/directory (again reiserfs) on the same NFS server, the
load stays fine.

When we run 200 processes locally on the server, writing to the
directory under the 3ware controller, again the load stays low.

Any insights would be much appreciated...


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Re: high load

[Andreas Behnert]

Phil Garcia wrote:
> Hi,
> 
> We've come across a problem that seems related to the interaction
> between NFS and a 3ware 7500-8 running RAID 5 with one hot spare.  We
> have a test program that opens a file and then loops, writing up to
> 255 bytes to the file and then sleeping for up to 10 seconds.  We run
> around 200 instances of the program simultaneously for about 25
> minutes.
> 
> When we run the processes on 200 separate slaves, writing to a
> (reiserfs) directory under the 3ware controller, the load on the
> server shoots up to over 20 and then gradually declines over the next
> 5 minutes or so.

The problem may be caused by ReiserFS:
If you are using kernel 2.2.x and ReiserFS 3.5.x - ReiserFS for
kernel 2.2.x is REALLY broken. We had similar problems here that
ended up in ReiserFS destroying itself, reproducible! Patches
from ftp.namesys.com didn't help at all. At that time ReiserFS
was nothing more than something to play with.
Can't say anything about kernel 2.4.x and ReiserFS 3.6.x - after
the 3.5.x desasters we moved back to ext2 and are now running ext3
with "data=journal" on our NFS servers without a single problem ...


Regards,
Andreas



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