[SCALE] Just a Mirror adding a disk Question

[peterge]

Hi, this is just a quick thought I want to have confirmed before doing it.
I am running 2x 14 TB disks in a mirror setup. One disk failed last month. I ordered a new one, and now I get a replacement next week.
I am thinking to upgrade my pool. Because I don't need the storage which a RAIDZ-1 would offer me (I have currently 50% used), I think about adding the disk to the mirror.

- Is it correct that clicking on Mirror ... and Extend and add the new disk (which is not connected yet) allows me to do what I want?
- If it's correct, I then have a setup, similar to RAID1 with three disks? So I can tolerate 2 drive fails, and gain no extra write/read bonuses?
I know a RAIDZ1 would be better suited, but I fear loosing a drive while resilvering is running....

Long story short: do I understand this topic correctly?

 

[LarsR]

you cant just add a new disk to a mirror and it magically becomes a raidz1. You would stripe your mirror with the new disk giving you a stripe of the mirror + the new disk. Buf if either the mirror or the single disk fails you pool will be lost.

If you want to change from mirror to raidz1 you have to backup your data, destroy the mirror pool and create a raidz1 from scratch.

 

[sretalla]

Long story short: do I understand this topic correctly?

Sort of...

If you add a third disk using the method you mentioned, you will have a pool that is a 3-way mirror, which does indeed allow for 2 disks of failure before any data loss would occur.

You will not have a RAIDZ1 without a complete rebuild of your pool (and I think you said you don't want that, so good).

I think it's fine, but the important part is to correctly extend (which at the command line is actually attach) the existing mirror and not add an additional single-disk VDEV in the process, which would be very bad.

You used the right terms in your original post to suggest you're on the right track.

 

[peterge]

Great, I think LarsR misunderstood me. Indeed, I want a 3-way mirror, which allows 2 disks failure before data loss.
I do not want a RAIDZ1.

I think it's fine, but the important part is to correctly extend (which at the command line is actually attach) the existing mirror and not add an additional single-disk VDEV in the process, which would be very bad.

How do I do that? Does this mean Extend on the Web is wrong? Can you guide me through the process? The disk should arrive tomorrow.
Thank you very much!

 

[sretalla]

How do I do that? Does this mean Extend on the Web is wrong?

The term extend is confusing in my opinion (since it's actually attach in the cli and you're attaching a disk to the mirror), but it's the correct option to select to get the job done.

Select the 3 dots on the mirror line and you'll be fine.

 

[peterge]

Select the 3 dots on the mirror line and you'll be fine.

We are talking about this extend correct?
Will try tomorrow and report back!

 

[sretalla]

Checking how it looks in the Status of the pool would also be good, just to make sure the 3rd disk is actually part of the mirror and not a separate VDEV. (I'm almost certain that will be the case, but both cases will result in the disk being shown as a pool member).

 

[peterge]

Checking how it looks in the Status of the pool would also be good

Looks good right?

 

[sretalla]

Looks good right?

Yes, perfect.