'zfs send/recv' during resilver/scrub

[Karli Sjöberg]

Hey all!

I posted this question on the forums yesterday but sending it here as
well to maybe reach a different audience:
https://forums.freebsd.org/threads/zfs-send-recv-during-resilver-scrub.53559/

A long time ago now, when I started writing my backup script called
'replicate', I had this notion that you shouldn´t do anything while
there was a resilver/scrub in progress, based on something I read that
was even older information. So the script halts if there is an ongoing
resilver or scrub in either source or destination system.

Now when searching for facts regarding this matter, I come up empty...
So thinking about it, is it really necessary? It might just be
superstition, based on old FUD that I´ve just been taking for granted.
Or have I been imagining this, and it has never been an issue in the
first place?

Thing is that with bigger, heavily loaded systems, scrubs and resilvers
can take days, even weeks, especially if it´s up at, say 80-90%
capacity. And to not have any recent backups for that long period of
time just isn´t right. So even if it could cause problems replicating
while there is a resilver or scrub running, it´s still preferable to not
having any backups.

How are others handling it, like FreeNAS e.g. Do they replicate while
scrubbing?

What are your thoughts about this?

Best Regards
Karli Sjöberg