ZFS - Abyssal slow on copying

[O. Hartmann]

Am Tue, 4 Oct 2016 12:42:32 +0200
Fabian Keil <freebsd-listen at fabiankeil.de> schrieb:

> "O. Hartmann" <ohartman at zedat.fu-berlin.de> wrote:
> 
> > Running 12-CURRENT (FreeBSD 12.0-CURRENT #32 r306579: Sun Oct  2 09:34:50 CEST 2016
> > ), I have a NanoBSD setup which creates an image for a router device.
> > 
> > The problem I face is related to ZFS. The system has a system's SSD (Samsung 850 Pro,
> > 256GB) which has an UFS filesystem. Aditionally, I have also a backup and a data HDD,
> > both WD, one 3 TB WD RED Pro, on 4 TB WD RED (the backup device). Both the sources for
> > the NanoBSD and the object tree as well as the NANO_WORLDDIR are residing on the 3 TB
> > data drive. 
> > 
> > The box itself has 8 GB RAM. When it comes to create the memory disk, which is ~ 1,3
> > GB in size, the NanoBSD script starts creating the memory disk and then installing
> > world into this memory disk. And this part is a kind of abyssal in terms of the
> > speed.  
> 
> Can you reproduce the issue if you replace the memory disk with
> a zvol or tmpfs?
> 
> While I agree that depulication could be the cause of the problem,
> it probably wouldn't hurt to rule out a memory-disk related issue
> before recreating the pool.
> 
> Fabian

I guess this issue was triggered due to having deduplication enabled on the ZFS pool
rather than on the ZFS partitions (this is a guess based upon comments made by knowing
people and the fact, that the noisy copying and slowness went away after removing dedup
from the ZFS pool).
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