Replacing Mirrored Drives in Older System

[RDM]

Hello,

I have a question, probably very easy but admittedly i am not as up on Free/TrueNas as I used to be.

I've been using it so long that my Raid 1 were state of the art 1.5 TB drives when i built my current system. So I wanted to grab a pair of 8-TB drives and replace them.

So my OS is on a Flash drive (latest version), and I only use it for storage and to run a Plex Media server. What is my path here?

Do I need to just rebuild it? Or can I replace the drives on the fly, realizing that I would lose all my data (not a big deal as I can replace)

Thanks in advance for any input or recommendations.

 

[sretalla]

If you add the new disks one at a time to the mirror and remove the old ones once complete, you'll be able to do it while everything is still running and lose nothing.

 

[RDM]

Wow. Thanks @sretalla. I always assumed that a RAID 1 config only had 2 drives? You are saying I could add drives one by one? And that they will resilver the new one? And then I could just remove the old ones? OK, I'm going to have to look that up because I don't see any RAID now in the UI. Like I said it's been a while. But thanks for that information!

Also I thought disks had to be same size?

 

[jgreco]

RAID 1 config

ZFS does not support RAID 1. It supports mirrors, which allow a variety of options such as going three- or four-way mirroring, so it is easy to attach a third (larger) device to the mirror, wait for it to resilver, then replace one of the other drives, wait for that to resilver, at which point you remove the third old (small) drive and your space suddenly grows to the size of the two new drives that are supporting the workload. Unlike RAID 1, there is no point at which your redundancy has been compromised if you do it this way.

 

[sretalla]

OK, well the documentation for this is missing completely at this point and I have exactly that same job waiting to be done at some point, so I'll take a couple of screenshots for you...

Storage | Pools | Cogwheel for that pool | Status:

Actually if you're paying attention this pool isn't already a mirror, but you can do the same thing with a mirror anyway...

3 Dots on one of the disks, then Extend.

Pick your new (larger) disk.

Let it resilver.

Do that again with the second one, then come back and Detach one, and then the other old one.

 

[RDM]

Man, thank you @sretalla (and others) for your time and effort!!!

This almost sounds too easy lol. Almost...

 

[sretalla]

One thing I would add/note having done that yesterday is that at the beginning, it just kind of sits there looking like it's not going to work... but if you're patient and just trust that it will eventually get there, it does.

General advice, patience and slow action is key, don't rush anything with ZFS.

 

[RDM]

@sretalla one more thing. I hate to beat a dead horse but. I was thinking and doing some reading. Does it even make sense to have mirrored ZFS volumes these days? Seems like they are pretty resilient. Plus, I don't think any of my drives has ever crapped out in years and years. Just seems to me that maybe I should just go with one. Do you agree?

If I were to go that route, could I still add the 8TB, resilver it and then "break" the mirror just leaving that drive?

 

[jgreco]

Plus, I don't think any of my drives has ever crapped out in years and years.

ZFS is intended as a resilient file system and you'd be kneecapping it by eliminating the redundancy. You can certainly do it, but you do have a few percent chance of losing your data in any given year, especially as the disks age. If your data isn't important and you don't care about it, then by all means ... but the flip side of that coin is, why are you even bothering to store it?

 

[sretalla]

Does it even make sense to have mirrored ZFS volumes these days?

Perhaps you're taking a hint from my non-mirrored pool above...

What I was in the middle of doing there was converting it from a stripe to a mirror (while increasing the size of the disks).

I had been using that pool for jails, so was satisfied that the loss of it would be easy to recover (by just re-creating my jails) since I don't store any data in the jails themselves. (and I back up to another pool which does have redundancy for the bits that matter in that pool).

I changed to mirror to avoid needing to mess around in the case of a drive failure (which hadn't happened in 4 years, but was always a possibility), having been more honest with myself about how much it would really take to get it al back how I like it and compared that to how easy it is to just resilver in a few drives.

 

[RDM]

OK guys, duly noted...thanks again for the quick replies. I will go ahead and add the bigger drives to my mirrored disks.