spa_namespace_lock and concurrent zfs commands

[Eugene Grosbein]

09.09.2020 19:29, Eugene M. Zheganin wrote:

> I'm using sort of FreeBSD ZFS appliance with custom API, and I'm suffering from huge timeouts when large (dozens, actually) of concurrent zfs/zpool commands are issued (get/create/destroy/snapshot/clone mostly).
> 
> Are there any tunables that could help mitigate this ?
> 
> Once I took part in reporting the https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203906 , but the issue that time got resolved somehow. Now I have another set of FreeBSD SANs and it;'s back. I've read the https://wiki.freebsd.org/AndriyGapon/AvgZFSLocking and I realize this probably doesn't have a quick solution, but still...

I think this is some kind of bug/misfeature.
As work-around, try using "zfs destroy -d" instead of plain "zfs destroy".

I suffered from this, too when used ZFS pool over SSD only
instead of HDD+SSD for L2ARC and used SSD sucked really hard
processing BIO_DELETE (trim) with looong delays.

Take a look at "gstat -adI3s" output to monitor amount of delete operations and their timings.