Replace all disks, keep old disks as backup?

[chemistocrat]

I have a Dell Poweredge R710 running 6x 3TB disks in raidz2. My pool is full, so I have purchased 6x 14TB disks.

I understand the official guidance is to replace the disks, one by one, then the pool will expand to use the full capacity of the new larger disks once all 6 disks are replaced.

My question is this: I would like to use those 6x 3TB drives as a last-ditch, something-has-gone-horribly-wrong, offline, offsite cold storage. Does this method leave those disks in a position to be added back to a TrueNAS system and a pool recreated from them? Or do I need to disconnect my existing 6x 3TB pool, remove all current drives, add the new 6x 14TB ones, and create a new pool from scratch?

 

[artlessknave]

once you have replaced them they will be free disks. you can do anything you want with them.

creating a new pool and replicating your data to it could be faster than replacing 6 disks one by one. up to you.

 

[chemistocrat]

creating a new pool and replicating your data to it could be faster than replacing 6 disks one by one. up to you.

I think I like this method better and I guess I don't really see why it would be necessary to do it one-by-one since this pool is just a backup for a NAS in my home.

So if I'm going to go that route, it's just a matter of disconnecting the current pool, swapping disks, and starting over then I'm assuming,

 

[Arwen]

No, the one at a time re-silver of a RAID-Zx does not allow the old disks to be brought back as a working ZFS pool.

Your only options are:

• Install the new disks, and make a new pool. Then ZFS send & receive the old pool to the new pool.
• Or replace the old disks 1 at a time. When done, create a new pool from the old disks and copy data back.

Now if you had a Mirror pool, different story. You can split the pool by removing 1 mirror disk from each vDev. This DOES allow using those disks as a working ZFS pool, which contains the exact copy of data at the time of the split.

 

[chemistocrat]

the one at a time re-silver of a RAID-Zx does not allow the old disks to be brought back as a working ZFS pool

replace the old disks 1 at a time. When done, create a new pool from the old disks

How are these two things different?

 

[artlessknave]

So if I'm going to go that route, it's just a matter of disconnecting the current pool, swapping disks, and starting over then I'm assuming,

only if you are starting over. as long as you can connect all the disks at the same time you can create the new pool and replicate to it. this would give you 2 identical pools. THEN you would do whatever you want with the old pool. they would be identical at that point.

 

[chemistocrat]

only if you are starting over. as long as you can connect all the disks at the same time you can create the new pool and replicate to it. this would give you 2 identical pools. THEN you would do whatever you want with the old pool. they would be identical at that point.

I've only got one TrueNAS machine with 6 drive bays, all of which are populated. So it seems it's either

a) replace/resilver disks one-by-one, or
b) replace all disks at once and have to rsync all data back to TrueNAS pool from my main NAS

Right now it seems like option b) makes more sense as it's unclear to me that option a) would even allow me to recreate a pool from the old replaced disks, which is an option I want to have. Disconnecting the pool seems like it it a sure way that I could recreate a pool from them in the future should something catastrophic happen, and it also seems like it might be the less time consuming route as resilvering one-by-one seems tedious.

 

[Ericloewe]

How are these two things different?

After replacing the disks, consider them empty, as far as recreating your pool goes.
Which is to say, you can of course use them, but need to create a new pool from scratch and populate it again.

 

[chemistocrat]

After replacing the disks, consider them empty, as far as recreating your pool goes.
Which is to say, you can of course use them, but need to create a new pool from scratch and populate it again.

I was misreading/misinterpreting what @Arwen had said. Thank you for clarifying, that makes sense.

I think for my intents I will disconnect the pool as it currently exists, swap all old disks with new disks, create a new pool with the new disks, and rsync everything from my production NAS to my TrueNAS system.

Thank you all for the help.

 

[artlessknave]

have to rsync

rsync is not the best option; replication is usually the best choice in most cases when it's available

machine with 6 drive bays

ah, yes, that would be limiting. the fastest way would be to start from scratch (unless you're going across the internet or something). in that case, you can definitely just export the old pool and have it as an offline backup.

 

[Arwen]

How are these two things different?

After replacing the disks, consider them empty, as far as recreating your pool goes.
Which is to say, you can of course use them, but need to create a new pool from scratch and populate it again.

What @Ericloewe said...

I had thought you wanted to preserve the old disks WITH data. Not possible with RAID-Zx pools. However, it is possible with Mirror vDevs using the zpool split option.

 

[chemistocrat]

I had thought you wanted to preserve the old disks WITH data

Yes, that is what I'm going for.

Just to clarify, is that not possible at all, or just when replacing disks individually? I was under the impression (as @artlessknave stated in the post immediately preceding yours) that if I disconnected/exported the current pool, it would act as an offline backup and I would in theory be able to import that pool again on any old TrueNAS system using all 6 of the old disks should I ever find the need in the future, however unlikely that may be.

 

[Arwen]

It is not possible to preserve existing data on old disks that have been replaced individually, when using RAID-Zx.

Yes, you can export the existing pool, and it will act as a cold / offline backup.
Yes, at some future date you can re-activate those 6 old disks in the old pool, if the need ever arises.

It is even possible to bring back a 6 disk RAID-Z2 pool with only 4 member disks fully functional. It's rare and requires manual intervention, but possible.


When replacing disks one at a time, (RAID-Zx or Mirroring), the data on the old disk(s) becomes out of date quite quickly. Even on a ZFS pool that has no writes. ZFS keeps track of it's pool members, so the simple act of replacing a disk with a new disk causes the old disk to be un-usable as part of that original pool. (As has been stated, the old disk can be used elsewhere, just that it's data is useless.)