Comment on ZFS: Should I use NAS or Enterprise/Datacenter SSDs?
lemmyvore@feddit.nl 11 months agoWhere can I read more about good ZFS settings for a filesystem on a new RAID6 array? I don’t want to manage disks or volumes with ZFS, I’ll be doing that with mdadm, just want ZFS as filesystem instead of ext4. I assume a ZFS filesystem can grow if the space available expands later?
yote_zip@pawb.social 11 months ago
ZFS can grow if it has extra space on the disk. The obvious answer is that you should really be using RAIDZ2 instead if you are going with ZFS, but I assume you don’t like the inflexibility of RAIDZ resizing. RAIDZ expansion is fully ready to be implemented into OpenZFS, but it will probably take a year or so to actually land in the next release. RAIDZ2 could still be an option if you aren’t planning on growing before it lands. I don’t have much experience with mdadm, but my guess is that with mdadm+ZFS, features like self-healing won’t work because ZFS isn’t aware of the RAID at a low-level. I would expect it to be slightly janky in a lot of ways compared to RAIDZ, and if you still want to try it you may become the foremost expert on the combination.
lemmyvore@feddit.nl 11 months ago
Right, I’d like to be able to add another disk and then grow the filesystem and be done with it.
Really, I’ll have to look into that then because health checks are my main reason for using ZFS over ext4.
mdadm RAID should be a transparent layer for ZFS, it manages the array and exposes a raw storage device. Not sure why ZFS would not like that but I don’t want to experiment if it’s not a reliable combination. I was under the impression that ZFS as a filesystem can be used without caring about the underlying disk support, but if it’s too opinionated and requires its own disk management then too bad…
yote_zip@pawb.social 11 months ago
The main problem with self-healing is that ZFS needs to have access to two copies of data, usually solved by having 2+ disks. When you expose an mdadm device ZFS will only perceive one disk and one copy of data, so it won’t try to store 2 copies of data anywhere. Underneath, mdadm will be storing the two copies of data, so any healing would need to be handled by mdadm directly instead. ZFS normally auto-heals when it reads data and when it scrubs, but in this setup mdadm would need to start the healing process through whatever measures it has (probably just scrubbing?)
turbo_scanning@feddit.de 11 months ago
Today, growing a pool is possible by adding a vdev, right?
So, instead of RAIDZ2, one could setup their pool with mirrored vdevs.
However, I’m not sure about the self-healing part. Would it still work with mirrored vdevs, especially when my vdevs consist of two physical drives only?