ZFS pool with a large number of filesystems

[Freddie Cash]

On Apr 4, 2016 6:16 PM, "Miroslav Lachman" <000.fbsd at quip.cz> wrote:
>
> Wim Lewis wrote on 04/05/2016 02:38:
>>
>> I'm curious how many ZFS filesystems are reasonable to have on a single
machine (in a single zpool). We're contemplating a design in which we'd
have tens of thousands, perhaps a couple hundred thousand, filesystems
mounted out of the same pool. Before we go too far into investigating this
idea: Does anyone have real-world experience doing something like that? Is
it a situation that ZFS-on-FreeBSD is engineered to handle with good
performance? Is there a rough estimate of the resources consumed per
additional filesystem (in terms of kernel VM and disk space)?
>>
>> Thanks for any insight or advice (even, or especially, if the answer is
"that's crazy, don't do that" :) )
>
>
> I donn't know about how many filesystems but I know that few hundereds of
snapshots can make a noticeable slowdown for some zfs operations.
>  I think that basic "zfs list" will be painfully slow with tens of
thousands of filesystems.
>
> Miroslav Lachman

Adding "-o <property1>,<property 2>,etc" to limit what you query via "zfs
list" really makes a difference. Especially on FreeBSD. PHK did a lot of
work optimising that a release or two ago.

"zfs list -o name -r -t all pool/fs"

is many many many times faster than

"zfs list -r -t all pool/fs"

Cheers,
Freddie

Typos courtesy of my phone.