ZFS pool multiple raidz2

[etnica]

Hello,
am planning for a truenas build and wonder if anyone have any input on this setup.

So basically I have 5 4TB drives ans 5 6TB drives. I am considering creating a pool with 2 raidz2 vdevs from these disks. Does this seem reasonable?

Seems the usecase usually is that all your disks is the same size :)

Cheers

 

[Spearfoot]

Hello,
am planning for a truenas build and wonder if anyone have any input on this setup.

So basically I have 5 4TB drives ans 5 6TB drives. I am considering creating a pool with 2 raidz2 vdevs from these disks. Does this seem reasonable?

Seems the usecase usually is that all your disks is the same size :)

Cheers

You're right, it's common practice to use the same sized disks in RAIDZ2 vdevs. Otherwise your capacity from each drive will be limited to the smallest disk in the vdev -- if you used all 10 of your disks in a RAIDZ2 vdev, it would be like using 10 x 4TB disks, giving you 32TB of capacity.

Your idea of using 2 RAIDZ2 vdevs would work, but you'll be sacrificing 4 of 10 drives for parity. This would give you 30TB of capacity, so you'd actually get 2TB more space just using all 10 drives in a single vdev.

The problem with a 10 disk RAIDZ2 vdev is that it's 'wide'.

If performance is what you're after, you could use mirrors:

• vdev1 = 2 x 4TB mirror
• vdev2 = 2 x 4TB mirror
• vdev3 = 2 x 6TB mirror
• vdev4 = 2 x 6TB mirror
• vdev5 = 4TB and 6TB mirror (the 'oddball')

This would give you 24TB of capacity altogether. Replace the 4TB disk in vdev5 with a 6TB disk to gain an additional 2TB.

Mirrors is what I would use in your situation.

 

[etnica]

Thanks for input.

Well my status is that the 5 6TB disks is running on a current NAS, so the plan is to build up a new NAS with the 4TB drives and move data over and then add the 6TB drives in a raidz2 to the new nas. i/o performance isn't an issue for me so I guess this will be fine then for my usecase.

Another question, the 80% rule of ZFS is that applied to a pool or a vdev? I will probably fill up the first vdev with over 80% but after adding a new vdev is this still a problem?

 

[Spearfoot]

Thanks for input.

Well my status is that the 5 6TB disks is running on a current NAS, so the plan is to build up a new NAS with the 4TB drives and move data over and then add the 6TB drives in a raidz2 to the new nas. i/o performance isn't an issue for me so I guess this will be fine then for my usecase.

Another question, the 80% rule of ZFS is that applied to a pool or a vdev? I will probably fill up the first vdev with over 80% but after adding a new vdev is this still a problem?

The limitation is by pool, but it sounds like you will exceed it on your 5-disk pool made up of 4TB drives. Adding an add'l vdev later won't fix this because ZFS doesn't magically redistribute data from a full vdev to an empty one.

Do you have a single, larger HDD? You could:

• Create a single-disk vdev made up of a disk large enough to hold all of your pool data
• Copy your pool data onto the new single-disk vdev
• Create a pool on your new server with the 10 drives
• Copy the pool data from the single-disk pool onto the new 10-disk pool

I use a single-disk pool this way as a backup scheme (see 'my systems' below). You could set up something similar on your new system.

 

[etnica]

Decided to downgrade from 10 to 8 disks instead.

So intitalt start will be a raidz2 vdev with 6 6TB disks(buying another disk) + 2 4TB disks. Will replace the 2 4TB later with 6TB ones, giving me ~32TB space when replaced.

This also means I will have enough disks for merging from the old NAS.

Leaves me with 4 leftover SATA connectors which I can use for something else in the future.

Maybe before the pool is full zfs support expansion of raidz(which I read an article about somewhere)