Disk drive upgrade path

[lightwave]

Hi!

I'm finally planning to retire my 8x1TB RaidZ2+spare array of more-than-a-decade-old Seagate Barracuda drives. My plan is to start with three 18 TB WD Ultrastar DC HC550 drives set up as a 3-way mirror and then, if I need additional storage, to add a fourth drive and convert the pool into RaidZ2.

If I understand things correctly, it should be possible to transform a 3-disk mirror to a 4-disk RaidZ2 without additional (temporary) storage and while still keeping at least two copies of the data at all times (i.e. allowing for one drive failure during the transformation). This is what I plan to do:

1. Remove one disk from the 3-disk mirror
2. Create a de-graded (2 drives missing) RaidZ2 on the new disk and the disk removed from the mirror
3. Copy all data from the (now) 2-disk mirror to the de-graded RaidZ2
4. Remove one more disk from the 2-disk mirror and add it to the de-graded RaidZ2. Wait for the pool to re-silver.
5. Clear the last disk from the mirror and add it to the de-graded RaidZ2 (which after re-silvering will no longer be de-graded)

Would this work, or am I missing something important here?

Thank you in advance!

Ps. I know I could set up a 3-disk RaidZ2 and use raidz expansion when adding the fourth disk. This would, however, mean a loss of capacity due to the existing data keeping its 2:1 parity to data ratio. Ds.

 

[danb35]

I know I could set up a 3-disk RaidZ2 and use raidz expansion when adding the fourth disk.

...assuming RAIDZ expansion exists in stable form by then. I don't know that I'd want to bet on that. Otherwise, your plan looks viable.

 

[Arwen]

Agree.

Your 3 disk Mirror vDev option is one that I am leaning towards for my home system. Thanks for reminding me that I can convert that 3 disk Mirror vDev to RAID-Z2 later if I want. (I do have 4 x 3.5" disk bays, SATA ports and power for a 4 x 3.5" disks.)

 

[Davvo]

It's my expansion plan as well, looks fine to me.

 

[lightwave]

@danb35, @Arwen and @Davvo: Thank you so much for your replies and for confirming that my expansion idea might actually work Then I will go ahead with a 3-disk RaidZ2 to start with.

 

[lightwave]

Agree.

Your 3 disk Mirror vDev option is one that I am leaning towards for my home system. Thanks for reminding me that I can convert that 3 disk Mirror vDev to RAID-Z2 later if I want. (I do have 4 x 3.5" disk bays, SATA ports and power for a 4 x 3.5" disks.)

I always assumed you ran a much larger setup. Something like a 50+ disk array on running on a 90-ampere power connection ;-) Kidding aside. What hardware are you running on?

 

[Arwen]

No. My work on the other hand does have some larger SAN / NAS setups. We even use ZFS on hardware RAID, which is normally a no-no. But, that's Solaris on enterprise grade SAN.

Have a small AMD Epyc setup, with 1 x 10TB disk at present. (But, 2 full backup disks & 1 backup disk without media.) It's time to buy another 10TB disk for the 1st mirror.


My NAS has archival static storage, but the main purpose of my NAS is another backup. All my computers have alternate boot media, with a full copy of the OS. It may be a bit old, though only months old. Plus, I have 2 backup disks that attach locally for backups. And all the computers use mirrored OS, with my desktop & newest laptop using ZFS Mirrored storage pool.