NFS issues since upgrading to 13-RELEASE

Rick Macklem rmacklem at
Thu Apr 15 20:47:27 UTC 2021

Allan Jude wrote:
>On 4/15/2021 9:22 AM, Chris Roose wrote:
>> I posted this in -questions and someone suggested I post here as well.
>> I'm having NFS availability issues between my Proxmox client and FreeBSD server (10G link) since upgrading to 13->RELEASE. And unfortunately I upgraded my ZFS pool to v2.0.0 before I noticed the issue, so I'm kind of stuck.
>> Periodically, the NFS server (I've tried both v3 and v4.2 clients) will go unresponsive for several minutes. I never had >this problem on 12.2, and as far as I can tell it's not a disk or network I/O issue. I'll get several "nfs: server not >responding, still trying" messages on the client and a few minutes later it usually recovers. It's not clear to me yet >what's causing the block. Restarting nfsd on the server will resolve the issue if it doesn't clear itself.
otis@ has run into a problem that sounds similar.
He sees a growing Recv-Q size on the server for the TCP connection from the client
when "netstat -a" is done on the server when the "hang" occurs.
In his case, he is using a Linux client and it does not recover, however other client
mounts continue to function.
I suspect the recovery after a few minutes is the client establishing a new TCP

He has been running for almost a week with r367492 reverted and has not reported
seeing the problem again (he had reported that it has taken up to a week to recur, so
reverting r367492 *might* have fixed the problem and I'd guess we'll know in another

- If using svn to revert the patch is inconvenient, I've attached a patch that can be applied
   to revert it.
- Alternately you can try rscheff@'s alternate proposed patch that is at
  I have not yet had time to test this one, but since I cannot reproduce the hang, I can
  only do testing of it to see that it is "no worse" than reverting r367492 for my

Please let us know which you choose and whether or not it fixes your problem.
>> Any pointers for troubleshooting this? I've been looking through vmstat, gstat, top, etc. when the problem occurs, but I haven't been able to pinpoint the issue. I can get pcap, but it would be from the hosts, because I don't have a 10G tap or managed switch.
>run `nfsstat -d 1` and try to capture a few lines from before, during,
>and after the stall, and that may provide some insight.
>Specifically, does the queue length grow, suggesting it is waiting on
>the I/O subsystem, or does it just stop getting traffic all together.

If the revert of r367492 does not fix the problem, monitor the TCP connection(s)
via "netstat -a" and, if possible, capture packets via
tcpdump -s 0 -w hang.pcap host <nfs-client>
or similar, run on the server.

Ideally the tcpdump would  be started before the "hang" occurs, but running
one while the hang is occurring (until after it recovers) could also be useful.

Thanks for reporting this, rick

Allan Jude
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