Basic question on growing a pool

[the_jest]

I have a FreeNAS system with one pool, consisting of two mirrored vdevs: a total of 4 4TB drives, so 8TB usable space. I use the system mainly for storing media files and backups at home, not for any high-performance or multiple-user needs. My case has 8 drive bays, so I have room for four more drives. This has been working fine for a few years, and I'm not facing an emergency situation, but it's probably time to consider expanding things before space does get tight.

The docs discuss this a bit in the Replacing Disks to Grow a Pool section, but it appears to miss a main concern: the preferred method is said to be adding vdevs, with the replacing-disk solution only used if you don't have any spare disk ports. However, it seems to me that even if I do have the ports (which I do), I wouldn't want to use them. If I get two larger drives and add a new mirrored vdev, I'd then have a pool with six drives, four of which are smaller-capacity and older, but I can't remove any of them because you can't remove a vdev (I think)--so I'd have to maintain six drives going forward.

I'd think that the right approach would be to follow the advice in the Replacing-Disks section to replace one vdev. I can then maintain four drives, but with more space; alternately I could leave the two existing drives in place and create a new pool from them, for some different storage task.

Does that make sense? And, this may be a(nother) silly question, but I'd get the space even by replacing only one vdev, right? That is, if I get two 8TB disks and use them to replace one vdev, I'd get more space; I don't have to get four drives to replace both mirrored vdevs?

 

[PhiloEpisteme]

That is, if I get two 8TB disks and use them to replace one vdev, I'd get more space; I don't have to get four drives to replace both mirrored vdevs?

You are correct. In fact, it looks like your understanding above is all generally spot on. The one thing to consider is whether maintaining 6 drives or not is a bad thing for you or not compared to 2 pools, 1 with 4 disks and 1 with two. What are specific concerns with the 6 disk pool?

 

[Jailer]

And, this may be a(nother) silly question, but I'd get the space even by replacing only one vdev, right? That is, if I get two 8TB disks and use them to replace one vdev, I'd get more space; I don't have to get four drives to replace both mirrored vdevs?

That is correct. You can replace just 2 drives to grow space in your pool with mirrored vdev's. Just make sure you replace the correct 2 drives when you do it. That's actually a simple cost friendly way to increase space for those that don't have it financial means to purchase a large number of drives at once to grow a pool.

 

[the_jest]

You are correct. In fact, it looks like your understanding above is all generally spot on. The one thing to consider is whether maintaining 6 drives or not is a bad thing for you or not compared to 2 pools, 1 with 4 disks and 1 with two. What are specific concerns with the 6 disk pool?

Only that I'd then have to maintain six disks going forward. When I really only need two, to be honest. With a six-disk pool, I have less space in my case, more power/heat, and four disks that are older and presumably more prone to failure; all this to keep using four drives that are smaller capacity (because I'd get larger drives as time goes on and prices go down).

The two-pool question was more of a lark, basically. The main pool would continue to be the, um, main pool. But I'd then have an extra pool to play around with, instead of pulling out two currently-functioning drives and putting them into a drawer. Yes, I know this conflicts with what I said above, but in this case it wouldn't matter too much if the second pool starts to die.

Anyway, now that we've established that my main plan will work, what are the best Black Friday deals for NAS drives? ;-)

 

[Jailer]

Anyway, now that we've established that my main plan will work, what are the best Black Friday deals for NAS drives? ;-)

Look for the WD elements to go on sale and shuck them. I paid $130 for each of my 8TB drives that I'm currently running.

 

[the_jest]

Look for the WD elements to go on sale and shuck them. I paid $130 for each of my 8TB drives that I'm currently running.

Is there any way to know what kind of drive is inside? Are they OK for a NAS? I assume these wouldn't be the Reds.

Amazon has the 8TB elements for $125 right now.

 

[Jailer]

I got one red and 5 white label. The white label may need a molex to SATA power adapter to get them to work depending on what power supply you have but are otherwise the same drives.