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Re: optimesing NFS Server for e.g. remote Backup





Götz Reinicke wrote:
Hi,

I have some RHEL4 servers and want to set up a central backup system
with a "big" harddisk. I found a very nice shell-script, doing
incremental backups using tar.

So I thougt, I'll mount the Backupserver-shares by NFS on the
"client"-servers and run the backupscript by cron so the servers write
there backupdata to the nfs shares.

My problem:
The tests I made where almost fine, but from time to time I do get errors:

/bin/tar: /export/backup02/shares-Wed.tar: Cannot open: Input/output error
/bin/tar: Error is not recoverable: exiting now

Any ideas what coul be wrong? The Backups are about 10 GB +- up to 100
GB in the future.
Various things and a dmesg on the NFS server exporting the backup partition of the "big" harddisk immediately after you get the error might give you a clue. If you either starve your NFS server as a result of too much I/O or you face networking issues between your NFS clients and the server could produce similar issues. I would start by checking that there are no issues with the LAN cards and generally the Ethernet segment that connects them. Pinging with large packet sizes from the clients to the server and vice versa should give you no packet loss. Some LAN cards also face issues with a large number of packets hitting the card and might lock up temporarily during periods of heavy activity.

The second Question: Which NFS/mount/export optimisation settings are
recomendet? (e.g. NFS Version, buffers...)
I think the best thing you could do is have a look at the official NFS-HOWTO at sourceforge
http://nfs.sourceforge.net/nfs-howto/performance.html

Neither I nor the document can give you the magic sysctl values and the most suitable mount options, but it will give you clues on what you might play with. IMHO, NFS does not scale beyond a certain point. We have a similar setup for file I/O with a 2 Tbyte share that we export on approximately 24 other servers for file dist purposes. Also, it would be good if you give NFS its own dedicated switch, very common for inter server I/O traffic...If that switch happens to be a capable managed switch and all your servers have 1Gbps cards , you might consider playing with jumbo frames (MTU > 1500)...

GM

Thanks a lot for any hints and tips!

Regards

Götz Reinicke

--
--
George B. Magklaras

Senior Computer Systems Engineer/UNIX Systems Administrator
The Biotechnology Centre of Oslo,
University of Oslo
http://www.biotek.uio.no/

EMBnet Norway: http://www.biotek.uio.no/EMBNET/



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