How Best to Expand Existing ZFS Pool

[DeterH]

Hello all, first time post and all it implies.

I would like to add a 5th disk to my current pool. What is the best way to achieve that? From what I've read, it's not possible to simply expand the pool by adding a disk. If I back up the data, delete the existing pool, add the new disk and create a new pool, what is the best configuration? Or, is this not the best approach at all? The MB has 6 SATA connections but I would like to use one for a SSD boot drive (currently a 16 GB USB stick) so should I give that up for a 6th drive? I know, a lot of questions but any help would be greatly appreciated.

• Motherboard make and model - Supermicro X10SLH-F
• CPU make and model - Intel Xeon E3-1226 V3
• RAM quantity - 16 GiB ECC
• Hard drives - 4 ea WD 6TB Z1 (please not data contained in pool is non-critical)

 

[SweetAndLow]

You can't add a disk to a vdev like you are wanting to do. You would need to backup the pool and recreate it.

 

[K_switch]

I would like to add a 5th disk to my current pool.

what @SweetAndLow said is correct... you can not add drives to any existing vdevs. Since zfs pools are comprised of vdevs (Virtual Devices) you could in theory create an additional vdev of just this single drive and add it to the existing pool... this configuration is not recommended outside of purely testing purposes.

My option would be that you purchase an additional drive to bring you up to 6 drives total... at that point you could configure your pool to have your current vdev of 4X6tb in RaidZ1 and a newly created vdev of 2X6tb Mirrored (NOT RECOMMENDED). Or you could backup the data and recreate the entire pool to either a 6X6tb in RaidZ2 giving you 20TB usable and double parity, you could also move to a 2 3X6tb RaidZ1 pool.

The latter are recommended :)

With your SSD i would recommend, depending on your current PCIe layout, you could use a PCIe m.2 adapter for your boot/SLOG/L2ARC if needed.

 

[DeterH]

SweetAndLow, thank you for the reply. I came to the same conclusion after doing some research but was unsure. Would Z1 be adequte for my purposes? Thanks too for the recommended reading - great resource.

 

[K_switch]

@DeterH

What are you using this FreeNAS system for?

 

[DeterH]

K_switch, that is some good advice. I was wondering if a m.2 drive would serve as a boot disk. Could you expand on the 2 3x6tb Z1 pool? Why not a 6x6tb pool?

 

[DeterH]

K-switch, the system is used as a file server for watching videos, viewing photos, and a central place to hold household documents for a two-person household. As such there is not a lot of demand on the server.

 

[SweetAndLow]

Raidz1 is not a good idea. To high of chance a disk will fail during a rebuild. Doing 6 disks in a raidz2 is a great option.

 

[Yorick]

It really comes down to: Those photos and household documents, where are they backed up? Is it no hassle, a small to medium hassle, or a large hassle to restore when your pool fails?

Like @SweetAndLow says, raidz1 is more likely to fail during resilver, whereas raidz2 is more likely to survive the rebuild.

 

[K_switch]

Doing 6 disks in a raidz2 is a great option.

@DeterH I agree once again with @SweetAndLow once again... the 6X6tb raidz2 will mean you will have better redundancy... since it seems there isn't a huge need for on demand read/writes your performance should still be exceptional... if you device to go the M.2 route i would possibly recommend partitioning that drive and do research on SLOG/L2ARC...

 

[SweetAndLow]

@DeterH I agree once again with @SweetAndLow once again... the 6X6tb raidz2 will mean you will have better redundancy... since it seems there isn't a huge need for on demand read/writes your performance should still be exceptional... if you device to go the M.2 route i would possibly recommend partitioning that drive and do research on SLOG/L2ARC...

With his workflow described there is zero need for a slog or l2arc. Plus the m.2 will not be a good slog.

 

[K_switch]

With his workflow

he mentioned moving to an SSD for boot... so i recommended the m.2... and since FreeNAS doesn't need all of the m.2 for boot i figured he could partition it out for some testing. that is all.

 

[SweetAndLow]

he mentioned moving to an SSD for boot... so i recommended the m.2... and since FreeNAS doesn't need all of the m.2 for boot i figured he could partition it out for some testing. that is all.

Don't do that. It's not going to work well.

 

[DeterH]

Guys, thanks for the discussion it's been really helpful and enlightening. It lead me to do further research that yielded the attached pdf article. According to page 6, although not the best solution, it would not out of the realm of acceptability to create a 5-wide RAIDZ1 pool. This would survive a single disk failure and I've experience such a failure in the past. FreeNAS is very good a letting you know when a disk is about to fail. The data contained in the existing pool is not critical and is periodically backed up on a PC as well as on MS One-Drive. So, no worries there.

Any further thoughts or suggestions would be greatly appreciated?

 

[DeterH]

OOOOPs, not question on last sentence. :p