SDB: NFS problems with the SuSE Linux Enterprise Server 8 for i- and pSeries

NFS problems with the SuSE Linux Enterprise Server 8 for i- and pSeries

Support knowledgebase (nfs_udp_sles8ppc)

Applies to

SuSE Linux PowerPC: Version 8.1

Symptom:

In some rare scenarios there is a small possibility of a data integrity problem when using NFS over UDP with standard parameters. The NFS server has to have high bandwidth links of more than 200 MBit/sec total for outbound data. In addition this bandwith has to be in use for the window of possibility to open. Services that run over TCP are not affected.

Cause:

There is a general problem with data fragmentation/reassembly within the IP definition. Fragmentation timeout and transport ratio has to be in a certain relation to be 100% safe. Please notice that all implementations of NFS over UDP are hit by that problem.

Solution:

Set down IP fragmentation timeout to three seconds:
```
        echo 3 > /proc/net/sys/ip_frag_timeout
     
```
This might cause problems when connecting to an other site over a slow latency WAN.
Avoid fragmentation: If you're running NFS over a line that supports jumbo frames please use them. Most GBit adapter and some 100MBit adapter should already do. To set that on e.g. eth4, type:
```
        ifconfig eth4 mtu 9000
     
```
If both of the above settings are not fit your environments you will have to reduce read/write block sizes to 1KBytes for NFS mounts.

Add the following options to your /etc/fstab or were mount options are defined (NIS/LDAP depending on your setup):
```
        rsize=1024,wsize=1024
     
```

Please be aware that there you will find an update OS kernel in the near future. This will give you the possibility to adjust ip_frag_timeout per outgoing device besides a couple of other changes that even lower the possibility of data corruption.

Keywords: NFS, UDP, PPC, ISERIES, PSERIES

SDB-nfs_udp_sles8ppc, Copyright SuSE Linux AG, Nürnberg, Germany - Version: 20. Mar 2003
SuSE Linux AG - Last generated: 20. Mar 2003 by snbarth (sdb_gen 1.40.0)