How to Raid with 3 drives

[leothaes]

Hi guys, hope someone can help.

So I have a single drive zfs pool using a 22TB Seagate Ironwolf pro. I have another 22TB drive (a Seagate Exos X22). I know I can add this to the pool as a mirrored drive, but I also need to increase my capacity, but will never do stripe.

I can obtain another 22TB drive for a total of 3.

Is there a raid configuration I could use similar to raid-5 where I can have the capacity of 2 drives while being able to lose one drive of the 3 without data lose?

And also, can it be done without destroying the existing data on the single drive?

 

[UdoB]

Is there a raid configuration I could use similar to raid-5 where I can have the capacity of 2 drives while being able to lose one drive of the 3 without data lose?

Sure: RaidZ. You get (approx.) the performance of a single drive and the capacity of two of them. Not recommended for VMs, only for "data".

(Actually Raid5 / RaidZ1 is not recommended at all nowadays - not with this large capacity. Always go RaidZ2...)

And also, can it be done without destroying the existing data on the single drive?

No. Not at this point in time. (Creating a mirror does work, RaidZx does not.)

Good luck

 

[leothaes]

It sounds like it would need to keep accumulating drives until I have enough to create a new pool then migrate the data. But I am afraid I may run out of storage before that.

Any suggestions?

 

[UdoB]

Was my "Sure: RaidZ." unclear?

It is not recommended, but it is technically possible. And it is exactly what you are asking for...

 

[leothaes]

Well you also replied to my question about if I could do it without destroying the data. So what I got from your response was that if change it to a mirror It shouldn't destroy the data, but moving to raidz wouldn't work work like that and I would end up destroying the existing pool. Is that correct? Or did I misunderstand?

 

[UdoB]

Or did I misunderstand?

No, unfortunately.

Sorry, I just didn't (re-) read my own post :-(

 

[leothaes]

So here's what I'm thinking. I currently only have 2 drives. I will add the second drive creating a mirror and let that run for now so I have some redundancy. Then I'd start buying drives until I have a total of 6. At that point I can remove one drive from the mirror so that I have a single drive pool and 5 unused drives. Create a new pool in z1 or z2 config then migrate the data from the single drive pool to the new pool. Finally, disconnect the drive from the single pool and keep it as a spare in case of a failure in the new pool.

 

[Kingneutron]

Or you can just leave it as a mirror pool and keep adding +2 disks. But yah, raidz2 starts making more sense around the 6-8 disk mark. Don't bother with raidz1 when you have disks over ~2TB size. 2 disk failures will kill your whole pool with raidz1.

Would also not recommend going down to a single-disk pool when migrating data from mirror to raidz2 unless you have a backup. Maybe look into tape drive for that

ALSO - make sure you do a burn-in test on ALL drives before putting them into use - this applies to New and Used drives.

https://github.com/kneutron/ansitest/blob/master/SMART/scandisk-bigdrive-2tb+.sh

NOTE that dd'ing zeros to the entire drive will destroy all data on it. You could use badblocks non-destructive mode, but be prepared to wait several days for that to finish