Hello all just had a quick question about extending mirror datasets. Sorry if this is the wrong place to ask. I haven’t been able to find a clear answer to my specific case and figured asking the community would be the fastest way to get an answer.
I recently updated my TrueNAS server by adding two eight-terabyte drives in hopes of expanding the amount of storage I have for Plex.
My current data pool for Plex is in a RAID1 configuration with two four-terabyte drives. I extended the vdev by adding the two eight-terabyte drives. I understand that resilvering the new drives takes time (on some posts I have seen upwards of three days).
In my case, the resilvering is complete but, the storage pool has not expanded. Screenshots have been attached below.
Is there something that I am missing?
Thank you and happy Mothers Day!
To be more exact, you went from a 2-wide mirror vdev to a 4-wide mirror vdev… which at the end of the day is still a single vdev with 4 TiB usable capacity. But hey! You got redundancy that can handle three drive failures!
You wanted to add another mirror vdev, which would then have your pool comprised of two vdevs:
2-way mirror (4 TiB) + 2-way mirror (8 TiB) = two vdevs total with 12 TiB capacity
You can still detach the two 8 TiB drives, “demoting” your vdev from a 4-way mirror back down to a 2-way mirror.
Then you can add an additional 2-way mirror vdev to your pool with those two (now liberated) 8 TiB drives.
Be careful. Even though it’s supported, you don’t want to do any mistakes that end up with a bad outcome.
Copy that. Thank you so much for the reply and for clearing up my confusion. I went ahead and detached those two disks and created another vdev for my storage pool.
I didn’t realize that you couldn’t extend a mirror vdev in that manner. Good to know moving forward.
A mirror vdev’s capacity is only as big as its smallest member.
In your situation, if you detached the two 4 TiB drives, then your existing mirror vdev can now hold 8 TiB usable capacity.[1](It’s no longer limited by the smaller 4 TiB drives.) You can then sell your 4 TiB drives, give them to a friend, or do whatever with them. You have just essentially doubled your pool’s capacity by expanding its sole, single mirror vdev, having (safley) replaced the smaller drives with larger ones.
But that is all beyond the scope of what you wanted to do: add an extra vdev to the pool itself
This assumes your pool has autoexpand enabled. Otherwise, you’ll have to issue the command manually to gain the extra usable space in the vdev(s). ↩︎
I hadn’t thought of replacing the 4TB drives with the 8TB but now that you mention it, I think that is a great idea!
I don’t add new content to Plex often so having four extra terabytes in that pool is more than enough. I have another media pool that I use as an archive for finished projects. That data pool is running low on storage so I will add those two drives as another mirror vdev.
In order to replace the four terabyte drives would I have to offline one at a time and then use the replace option in the pool status menu?
As long as your pool is comprised only of stripes of mirrors, you can remove the two-way 4 TiB mirror vdev.
The data will be copied over to the other mirror vdev (two-way 8 TiB).
I’ve never done it, and I’m not even sure what the implications are if you face a sudden powerloss during this process.
EDIT:
On second thought, this is the safer route. You’ll essentially be doing what you did before (creating a four-way mirror), and then removing the 4 TiB drives, one at a time.
Kind of like this, starting from the point you had a four-way mirror...
A mirror vdev’s capacity is only as big as its smallest member.
In your situation, if you detached the two 4 TiB drives (from your four-way mirror), then your existing mirror vdev can now hold 8 TiB usable capacity. (It’s no longer limited by the smaller 4 TiB drives.) You can then sell your 4 TiB drives, give them to a friend, or do whatever with them. You have just essentially doubled your pool’s capacity by expanding its sole, single mirror vdev, having (safley) replaced the smaller drives with larger ones.
