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nfs write problems



So, I have a relatively new system on which I am seeing strange NFS behavior.

In short I am getting seemingly random errors in files written via NFS.

   * I do not get the errors if I write files locally.
   * I have no errors in the NIC, I even tried a second NIC in a PCI
     slot as opposed to the onboard one. There are no errors recorded
     on the NIC or the switch on a 1Gb port.
   * I see no memory errors, I ran memtest for 3 days clean.
   * To test I am using dd if=/dev/zero of various (large) file sizes.
   * Since I know that the file should be all zeros I wrote a C program
     to read it back and tell me where it finds non-zero bytes. The
     program results are confirmed with od.
   * The files read back always have the errors in the same place, so
     it is not a problem with reading the files.
   * There are no errors in any logs.
   * The problem occurs on both the RAID1 (ext3) and RAID10 (xfs)
     filesystems.
   * I've tried two clients, both FC5 one 64bit, and the other a 32 bit
     with the same results. This error was uncovered by users
     attempting to write files from other systems and other Fedora
     releases, so it is repeatable regardless of the client.
   * the server is not running anything else and spends a large portion
     of the time idle. loadaverages are quite low. swap is mostly
     unused. a large portion of RAM is allocated to file cache, but I
     expect that this would be normal for this amount of file IO.

The server is running an up-to-date FC6, although this also occurred with FC5. I am about to try F7.

Hardware is an AMD 1220 dual core 64bit, on a Tyan K8SSA S3950
with an Adaptec Raid 2230SLP and 7 Fujitsu MAU3147NC.
The RAID config is that 1 disks (on diff channels) are in a Mirror for the OS, 4 are in a Raid 10 config and 1 is a hot spare.

Anyone ever seen anything like this before?
Suggest where I might look next?
Additional tests?


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