zfs recv causes nfs server to throw NFSERR_IO i/o errors

[Daniel Genis]

Hi everyone,

we've been tracing an issue where snapshot replication is causing
interruptions for the NFS serivce.

The problem is as follows:

Every time a zfs recv finishes, there is a chance for the NFS server to
return an NFSERR_IO for a GETATTR call. This shows up as input/output
errors on the nfs clients.

Here the tcpdump showing the NFS conversation:
https://nopaste.me/view/95d1a79d

NFS 202 V3 GETATTR Call (Reply In 6043), FH: 0x8c711a60
NFS 98 V3 GETATTR Reply (Call In 6042) Error: NFS3ERR_IO
NFS 222 V3 LOOKUP Call (Reply In 6046), DH: 0x6694634f/example.file.txt
NFS 102 V3 LOOKUP Reply (Call In 6045) Error: NFS3ERR_ACCES

We've been able to verify that there is a _direct_ correlation between
the zfs recv command and these NFS errors. For every input/output error
we can find a log entry of a replication just finishing (zfs recv exiting).

The receiving server is running 10.3-RELEASE

I've read about a VFS/ZFS deadlock issue which is to be included/fixed
in Freebsd 11.0-BETA4.

Could our issue be related?
Otherwise does anyone have any suggestions how to tackle this issue?


For the record, say we have two volumes:
tank/volumeA and tank/volumeB

If there is a zfs recv busy for tank/volumeA then tank/volumeB can get
these NFS "io" errors, it does not have to be the same volume.


Has anyone else seen/experience this as well?

Any insights are appreciated!

With kind regards,

Daniel

_______________________________________________
freebsd...@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/freebsd-stable
To unsubscribe, send any mail to "freebsd-stabl...@freebsd.org"

[Alan Somers]

Try adding mountd_flags="-S" to /etc/rc.conf.

[Daniel Genis]

Thank you, that probably is what the doctor ordered!
My quick testing shows that it's very likely fixed. Kudos! :-)

[Alan Somers]

Glad to help. BTW, that setting is the default in FreeBSD 11.