[Beowulf] NFS & Scaling issues

Joe Landman landman at scalableinformatics.com
Fri Apr 6 23:09:20 EDT 2007


Hi Amrik:

Amrik Singh wrote:
> Hi,
> 
> We are running a cluster of 180 diskless compute nodes. 60 of them have 
> 32 bit AMD Semptron processors and rest are  dual core AMD Athelon 64 
> bit processors. 32 bit machines have 10/100 mbps and rest have gigabit 
> ethernet cards. We have four file servers, each hosting around 3.5TB on 
> SATA drives connected to 3Ware RAID controller cards configured on RAID 
> 10 array. These file servers are exporting the drives through NFS. Each 
> file server is running 265 daemons for nfsd.
> 
> The file servers are mainly hosting large number of small files ranging 
> from 256KB to 2 MB. The compute nodes are primarily doing a search 
> through these files, so there is lot's of reading and some writing to 
> the file servers.
> 
> Recently we started noticing very high (70-90%) wait states on the file 
> servers when compute nodes. We have tried to optimize the NFS through 
> increasing the number of daemons and the rsize and wsize but to no avail.
> 
> Can someone point us in the right direction as to how we should be 
> trying to troubleshoot this problem.

You might want to look at the read patterns.

> 
> PS: All the nodes are running SuSE 10.0 and servers are running SuSE10.0 
> and 10.1 and all the drives are formatted with reiserfs.

Hmmm... I remember Reiser has had a problem in the past when file 
systems get full or nearly so.  There are file tail optimizations you 
might want to turn off, as well as use noatime for mounts.  I might 
suggest turning to a better file system for your servers (if possible, 
it might not be a trivial undertaking), but even then that might not be 
responsible.

Grab a copy of atop (google for it), run it on your file server.  See if 
it is the file system that is problematic (disk devices running near 80% 
or higher capacity for reads/writes all the time).

Other possibilities are your file access patterns, what the file server 
is doing itself, whether or not your networks are being flooded with 
small packets (see if your csw is very high, or the number of interrupts 
or packets are very high).

Joe

> 
> 
> thanks
> 

-- 
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: landman at scalableinformatics.com
web  : http://www.scalableinformatics.com
phone: +1 734 786 8423
fax  : +1 734 786 8452
cell : +1 734 612 4615
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