[OmniOS-discuss] Request advise on pool upgrade

[Andries Annema]

Hi guys,

Could you please give me some advise on the best way to increase the 
capacity on my home server (running OmniOS obviously...)?

About four years ago I started designing and building my home storage 
server based on a "Coolermaster Stacker" tower case by retrofitting into 
it three Norco SS-500 and one SS-300 hotswap modules, for a total of 18 
hard drives.
With this number of drive bays available, I choose to go for RAIDZ2: 
three vdevs of six drives each.

Back in 2014, I started with only one vdev of six 4TB WD40EFRX drives. 
About a year later, in early 2015, I put another six of those drives in 
and expanded the pool. It has been humming happily ever since. Awesome.

Over time however, the used pool capacity has now gone up to 86%. It's 
time to expand again.
I see a number of possible ways to do so:

 1. Get another six 4TB WD40EFRX's and fill the last open bays, adding a
    3rd vdev (capacity +50%).
    Pros: these drives are cheap nowadays, much cheaper than they were
    three or four years ago.
    Cons: six extra spindles will increase electricity cost.
 2. Get six 8TB WD80EFZX's and fill the last open bays, adding a 3rd
    vdev (capacity +100%).
    Pros: huge capacity increase.
    Cons: higher upgrade cost than option 1 (due to more expensive
    drives). Six extra spindles will increase electricity cost.
 3. Get six 8TB WD80EFZX's and *replace* the first vdev with bigger
    disks (capacity +50%).
    Pros: amount of spindles doesn't change and thus electricity cost
    will more or less remain the same. Replaced drives can be utilized
    elsewhere, e.g. for offline pool-backups.
    Cons: higher upgrade cost than option 1 (due to more expensive drives).

The first question that comes to mind for option 2 and 3: are there any 
disadvantages to creating a pool out of different capacity drives? The 
drives per vdev are identical, it's just the vdevs within the pool that 
aren't.

Right now I am leaning towards options 2 or 3, with maybe a little 
preference for option 3, I think.

Any thoughts you guys can share on this matter? Would appreciate it. Thanks!

Regards,

Andries

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