NFS reads vs. writes

[Karli Sjöberg]

Den 3 jan. 2016 4:01 fm skrev "Mikhail T." <mi+thun at aldan.algebra.com>:
>
> I have two similar 10.2-STABLE machines mounting each other's
> filesystems via NFS: a:/a and b:/b
>
> When moving some large files around today, I found a huge discrepancy
> between writing and reading over NFS. That is, machine a copying files
> from its own /a to NFS-mounted b:/b was pushing measly 2-3Mb/s over the
> Ethernet. When I cancelled that, logged-in to machine b and proceed to
> copy from a:/a to the now-local /b, I got 56Mb/s. I tried changing the
> wsize and rsize options, but it did not seem to make a difference...
>
> Any ideas, what is happening here? Why are NFS-writes some 25 times
> slower here, than reads? Both filesystems are zfs-backed (though with
> different options), both systems are plugged into the same switch, both
> use mtu of 9000.

The difference between "mount" and "mount -o async" should tell you if you'd benefit from a separate log device in the pool.

/K

>
> Thanks! Yours,
>
>     -mi
>
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