Adding capacity, how would you do it?

[BrennanK]

I currently have 4 - 3TB drives in a zraid2 in a 12 bay server. I am looking to expand my array by adding more drives. In an ideal world I'd like to see all the storage appear as one drive, but if that is not possible that is fine.

I would like to add more drives, probably 4 more. Should I extend the current volume? Should I just make a new vdev and volume? I have been reading around about extending a volume and I am having a hard time following how the redundancy is handled. From what I gather I would loose some redundancy if I decided to extend the volume - is that correct?
If it matters I have 850GB free of 5TB used.

 

[CraigD]

By adding another volume you have two "drives"

You could add extend by adding another 4 drive RAIDZ2 vdev and have 4 drives worth of parity

I would copy the data and break the 4 drive RAIDZ2 and create a 8 drive RAIDz2 then copy the data to it and have 2 drives worth of parity

Playing around in a VM test machine is a good way to learn try adding 8 10GB drives to a freeNAS VM machine and set them up it different ways so you know how to do it and roughly know what space you will have

Have fun

 

[Jailer]

Your redundancy is dictated by the layout of your vdev. If you expand your pool with an additional vdev of similar redundancy you don't compromise your pool. It's when you stripe a single drive to your pool that your redundancy is compromised.

For performance reasons you should keep the same vdev layout when expanding your pool and adding additional vdevs. It's not required but highly recommended.

This is why planning your storage arrangement before you begin building, including any additional expansion, is so important.

 

[Spearfoot]

I currently have 4 - 3TB drives in a zraid2 in a 12 bay server. I am looking to expand my array by adding more drives. In an ideal world I'd like to see all the storage appear as one drive, but if that is not possible that is fine.

I would like to add more drives, probably 4 more. Should I extend the current volume? Should I just make a new vdev and volume? I have been reading around about extending a volume and I am having a hard time following how the redundancy is handled. From what I gather I would loose some redundancy if I decided to extend the volume - is that correct?
If it matters I have 850GB free of 5TB used.

You could expand the capacity of your existing pool by expanding it with another vdev of 4 drives. But I wouldn't do that... I would destroy the existing pool and create a new one with all 8 drives in a single RAIDZ2 vdev.

Why? Because of space efficiency. Your current pool uses 50% (2 of your 4 drives) of the total disk space for parity. That's safe, but not very efficient. Adding an additional RAIDZ2 vdev of 4 drives would double your available capacity -- but you'd still be sacrificing 50% of your space to parity, using 8 drives to get 4 drives' worth of space. Ouch!

An 8-disk RAIDZ2 vdev would give you 6 drives' worth of space, using only 25% of your total disk space for parity. Much better! Add 4 drives to your existing 4, but triple your capacity!

Ah, ha! I see that @CraigD has posted the same idea. Dooooh! :)

EDIT: Of course, you need a good backup before destroying/re-creating your pool...

 

[gpsguy]

Another thing to keep in mind is that you have a 12 bay server.

One popular configuration is to have 2 - 6 disk RAIDz2 vdev's, striped together to form one volume.

While less efficient than 8 disks in a RAIDz2 vdev, having 6 disks in a RAIDz2 vdev allows you to add another 6 disk RAIDz2 vdev and extend your current volume. Or, if you want to grow an existing volume by replacing the disks, one at a time (and resilvering), you only need to replace 6 disks, before you see the additional storage.

With 8 disks in RAIDz2, if you want to use the other 4 bays, one option might be to add another volume (perhaps 2 sets of mirrors striped together). Or, backup the system again and start over with an 11 drive RAIDz3 volume.

 

[Stux]

I'd suggest getting two more disks and switch to a 6 disk setup. Then in the future add another six disks.