Hi All,

We have been struggling with what appears to be a bug in RH kernels.  
This results in local disk I/O blocking all NFS I/O (and, as we show, 
subsequent local I/O).  This appears easy to reproduce:
----
1.test access from the nfs server to the exported disk:
[root@server]# time touch /mnt/disk/testlocal
2.test access from an nfs client to the nfs mounted disk:
[root@client]# time touch /nfs/server/disk/clienttest
3.start local I/O on the nfs server:
[root@server]# dd if=/dev/zero of=/mnt/disk/zero bs=1K count=10M
4.while the dd is running, test I/O on the nfs server to the exported 
disk:
[root@server]# time touch /mnt/disk/testlocal2
5.while the dd is running, access the exported disk from the nfs client:
[root@client]# time touch /nfs/server/disk/clienttest2
6.one last time, while the dd is running, test access to the exported 
disk from the nfs server:
[root@server]# time touch /mnt/disk/testlocal3
----

After these steps, the last two 'touch' commands take anywhere from 30 
seconds to 3 minutes to complete.

We have reproduced this using ext2, ext3, and jfs; with and without 
lvm, scsi, and RAID; and with various RH kernels on RH9, RHEL3, and 
FC3.  However, RH7.3 does not have this same problem.

We opened a bugzilla bug 
(https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=139937), but have 
not yet gotten any resolution.  For the time being (and on disk servers 
where it is possible) we are restricting local logins to avoid running 
into this.

Has anyone on this list experienced similar problems?  If so, what have 
you done about it?

Thanks in advance for any thoughts.

Devin

--------------------
Devin Bougie
Laboratory for Elementary-Particle Physics
Computer Group
[log in to unmask]