FreeNAS + ZFS for redundant pooling?

Question

We currently have a box with 2 1 TB hard drives in, yesterday I installed FreeNAS and have been playing with the functions, its a very nice bit of software but I'm a little confused by the pooling aspect.

By the end of the year I'd like to have 6 drives in the machine (it can handle it, I checked) of varying sizes from 500gig to 2TB.. I'd love all the space to be pooled into one folder /pool and of course have the data spread out so if a drive dies.. I can swap the backup one next to it in without too much of an issue..

A lot of the ZFS tutorials for FreeNAS seem to have been written over a year ago when ZFS was in the beta stage.

At the moment the easist thing for me to do looks to be installing Window Home Server with its drive extender but that seems to have been EOL'ed and removed from the latest beta so in a year or two we would have to start all over again.

So at the moment I'm looking for advice, what should I do?

Answer 1

Sounds like you should consider ZFS mirroring. Start off with a mirror of the 1TB disks you have now and then when you add additional drives, add mirrored pairs of same-sized disks too the pool. Once you've filled all six drive bays, you can replace the smaller disks with larger ones and increase overall pool capacity (e.g. replace a 500GB disk with a 2TB disk and let it resilver. Then replace the 2nd 500GB disk with a 2TB disk and let it resilver. On next mount you'll have 1.5TB more free space.

RAIDz is fine if you have a lot of data and want to maximize your available space (at the expense of CPU overhead, IOPS performance and expandability) but with RAIDz (like RAID5) you need to have equal sized disks (or wasted space) and decide how many disks you want in the set at creation time. Technically, with 6 disks you could start with a 3 disk RAIDz with equal sized drives and when expanding you could add a second 3 disk RAIDz set, but life's too short for stupid things like that. Just go with mirroring.