zfs meta data slowness

[mike tancsa]

On 7/22/2020 1:04 AM, Rick Macklem wrote:
> mike tancsa wrote:
>> Hi,
>>    Thanks for the response. Reply in line
>>
>> On 7/20/2020 9:04 AM, Ronald Klop wrote:
>>> Hi,
>>>
>>> My first suggestion would be to remove a lot of snapshots. But that my
>>> not match your business case.
>> As its a backup server, its sort of the point to have all those snapshots.
> I'm the last guy who should be commenting on ZFS, since I never use it.
> However, it is my understanding that ZFS "pseudo automounts" each
> snapshot when you go there, so I think that might be what is taking
> so long (ie. not really meta data).
>
Thanks Rick, in this case, its just listing snapshots from the command line

zfs list -t snapshot

that is taking forever.

Best case scenario when the box boots up after running it once, it will
take about 25 seconds

but when the box is taking in zfs streams, it really slows down and can
be anywhere up to 30min


0{backup4}# time zfs list -t snapshot > /tmp/snap.out
1.839u 23.211s 3:11.69 13.0%    71+178k 2504801+38io 0pf+0w
0{backup4}# time zfs list -t snapshot > /tmp/snap.out
1.817u 23.612s 0:25.47 99.8%    71+178k 2472088+38io 0pf+0w
0{backup4}# time zfs list -t snapshot > /tmp/snap.out
2.040u 23.314s 0:25.40 99.8%    71+177k 2472105+38io 0pf+0w
0{backup4}#