Setting up RAID ZFS with plans to expand (Have 4x8tb, obtained 4x16tb, want both working together)

[DaGeek247]

Hey Y'all,

 

I've heard some pretty mixed reviews about how expandable ZFS setups actually are, and want to get it clarified before I start using it over mdadm raid.

 

I currently have four 8tb drives in raid5. It's been relatively great (with some hiccups happening before i figured out I'm, supposed to manually scrub the raid5 pool). I just bought four more 16tb drives for my server. My original plan was to move the 4x8tb setup to a small NAS to my parent's house for offsite backup after migrating all my data to the new 4x16tb pool on my server.

 

However, I heard that ZFS could do multi-size drives in a single pool, and 96TB of total space (which should have about 72tb usable) actually sounds really great to me. I could buy a cheap ssd, set up raid1 on a nas, and only backup my small important date offsite instead.

 

The problem is that I can't find any forum posts about how a ZFS pool with 4x8tb and 4x16tb would actually work. I don't want two separate storage listings, that would make the rest of my projects much more of a hassle than not having 72tb of usable space would do for me.

 

So my question is this; could I migrate my data from my raid5 4x8tb pool to a zfs 4x16tb pool, and then add the 48tb pool to the zfs pool afterwards, without having to move it all from backup? If yes, what would that look like?

 

Are there any risks that i'm missing out on (beyond the obvious moving data is dangerous risks)? What could redundancy look like in this situation?

 

Any help is appreciated.

[Electronics Wizardy]

Do you have 8 drive bays and want to add the 4 16TB disks?

 

If that's the case it should be pretty simple to run zpool add raidz1 /dev/sda /dev/sdb /dev/sdc /dev/sdd but with the actual drive letters you have. Then you basically have a raid 50 with 72TB total usable, and all of your existing data on it already. 

[SpaceGhostC2C]

As far as I understand, you can expand your current pool with a second vdev. Not sure if there's any consequence from not having the same capacity across vdevs, but I seem to remember it's not that important.

Having 2 vdevs in one pool is like having a "raid0"  (stripe) over your two "raid5" (raidz1) vdevs. If you do that, each vdev will survive losing a drive, and the pool would survive losing 1 drive in each vdev, but losing two drives in the same vdev would kill the whole pool.

 

I think raidz expansion has been announced but no yet available, or not universally. You can theoretically do a "migration-expansion" by creating a new pool in a degraded state right from the start, copying the data to it, then restore the pool integrity by adding the old drives as replacements for the "missing" drives - and you still would have the size mismatch problem in your case.

[DaGeek247]

3 minutes ago, Electronics Wizardy said:

Do you have 8 drive bays and want to add the 4 16TB disks?

 

If that's the case it should be pretty simple to run zpool add raidz1 /dev/sda /dev/sdb /dev/sdc /dev/sdd but with the actual drive letters you have. Then you basically have a raid 50 with 72TB total usable, and all of your existing data on it already. 

Yes, it will all be in the same computer. Zfs can add mdadm raid drives to a pool without losing data?

[Electronics Wizardy]

2 hours ago, DaGeek247 said:

Yes, it will all be in the same computer. Zfs can add mdadm raid drives to a pool without losing data?

I thought you had a raid5/z1 in zfs already.

 

If you want that config in ZFS from your current config, I'd make a raidz1 of the new bigger drives, then copy the data, then move the old drives to the new pool

[DaGeek247]

13 hours ago, SpaceGhostC2C said:

Having 2 vdevs in one pool is like having a "raid0"  (stripe) over your two "raid5" (raidz1) vdevs. If you do that, each vdev will survive losing a drive, and the pool would survive losing 1 drive in each vdev, but losing two drives in the same vdev would kill the whole pool.

Thank you, this is exactly what i was looking to know.

 

11 hours ago, Electronics Wizardy said:

If you want that config in ZFS from your current config, I'd make a raidz1 of the new bigger drives, then copy the data, then move the old drives to the new pool

That's what i had thought at the beginning. It eould be kinda neat if you could import an mdadm array inyo a zfs array while keeping the data on it though.