Re: Desperate with 870 QVO and ZFS

From: Eugene Grosbein <eugen_at_grosbein.net>
Date: Wed, 06 Apr 2022 11:42:53 UTC 
06.04.2022 18:18, egoitz@ramattack.net wrote:

> Good morning,
> 
> I write this post with the expectation that perhaps someone could help me :)
> 
> I am running some mail servers with FreeBSD and ZFS. They use 870 QVO (not EVO or other Samsung SSD disks) disks as storage. They can easily have from 1500 to 2000 concurrent connections. The machines have 128GB of ram and the CPU is almost absolutely idle. The disk IO is normally at 30 or 40% percent at most.
> 
> The problem I'm facing is that they could be running just fine and suddenly at some peak hour,
> the IO goes to 60 or 70% and the machine becomes extremely slow.

You should run: gstat -adpI3s
And monitor all values, especially "deletes": d/s, next KBps and ms/d.

If you have many delete operations (including ZFS snapshort destroying),
it may result in massive chunks of TRIM operations sent to SSD.
Some SSD products have abysmal TRIM performance.