ZFS on FreeBSD 11.3 slower than 10.4

[Miroslav Lachman]

On 2020-05-23 22:11, Walter Cramer wrote:
> On Sat, 23 May 2020, Miroslav Lachman wrote:
> 
>> I upgraded my old desktop computer few month ago from old 10.4 based 
>> PC-BSD to stock FreeBSD 11.3. It uses single 2TB HDD 7200rpm.
>> My problem is that upgraded version is really slow and some desktop 
>> applications are very lagging (playing multimedia is interrupted for a 
>> fraction of seconds) when there is heavy filesystem activity.
>>
>> I am using zfsnap2 for taking snapshots periodically and when there is 
>> enough snapshots zfs destroy is called. In this time the user 
>> experience is terrible. Starting new application like browser or even 
>> something much smaller takes minutes. The old version based on FreeBSD 
>> 10.4 behaves much better. I used the old version for years and never 
>> have problems with interrupted multimedia playback.
>>
>> Are there some sysctls to tune to get better desktop interactivity in 
>> heavy filesystem operations like zfs destroy, pkg check or other 
>> "find" periodic scripts?
>>
>> Kind regards
>> Miroslav Lachman


> 
> Does `top` or `vmstat` show that Free Memory is quite low when you are 
> experiencing the problem?  We had ARC / Free Memory performance problems 
> with 11.X, and found that setting the sysctl "vfs.zfs.arc_max" much 
> lower was necessary.

Free memory is not a problem.
The machine in question has vfs.zfs.arc_max="1024M" (the same as in 10.4)

Kind regards
Miroslav Lachman