@frb94 Just leaving it on 24/7 winter is here now or so we thought (its 75f outside today) . If there is any update on this i would try again. but as it seems you are having the same issue i did then, it does not appear to be fixed.

@acebmxer Thank you.

Just as an update on this. Did get the migrations working. Still haven't gotten the backups working. Pool is still stable otherwise. Have managed to get backups by using Veeam so it's not to much of a problem.

@poddingue said: While you experiment, do the failing VMs have something in common? The same source SR, for example, or a mirror target keeping a different retention than the source. There are two backup jobs that are failing. One from Ark (local) to Synology, and one from Ark to S3. It seems to be the same VMs failing each night, but interestingly, there are some that fail to Synology but succeed to S3 and vice-versa. There are 9 VMs that fail for both. They do not all share the same SR. The backups on Ark are coming from several delta jobs that run daily, weekly, and monthly. Retention are different for all those.

Thanks for the information, @ph7 . That's a typo, for sure.