ZFS performance as the FS fills up?

[Patrick M. Hausen]

Hi, all,

we use a big JBOD and ZFS with raidz2 as the target
for our nightly Amanda backups.

I already suspected that the fact that the FS was > 90% full might
be the cause of our backup performance continously decreasing.

I just added another vdev - 6 disks of 750 GB each, raidz2 and the
FS usage is back to 71% currently. This was while backups were
running and write performance instantly skyrocketed compared to
the values before.

So, is it possible to name a reasonable amount of free space to
keep on a raidz2 volume? On last year's EuroBSDCon I got
the impression that with recent (RELENG_8) ZFS merges
I could get away with using around 90%.

Thanks,
Patrick
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