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Montreal, QC
reply to elwoodblues

Re: Hard Drive Deals

That's what friends are for.

I'm waiting for a 4TB Red to become available at or near $100 :P It will be a while, so I'm hoping my existing 10x2TB can last that long.

Originally I was going to add five 3TB drives to my array, taking it from 20TB to 35TB, but then I had the idea that I can convert from raidz to raidz2 (like going from RAID-5 to RAID-6) in my next upgrade if I switch to 4TB drives and use 7 of them. My plan looks like this now:

1) Start with 10x2TB and 5xEmptySlot

2) Take 5 of 7 of the 4TB drives and put them in as a degraded 7-disk raidz2 array

3) Copy (zfs send) the data from the existing 10x2TB pool (16TB usable) to the 7x4TB pool (20TB usable)

4) Pull all the 2TB drives (they are still a consistent copy of the pool until I'm done the migration), and add the remaining 4TB drives

5) Resilver (rebuild the array). If it is successful, it means we now have a fully consistent copy of the original data and the old 10x2TB pool is no longer required. If it fails, start over from the beginning (since the 10x2TB at this point still has a consistent copy of all data).

6) Add back in 8x2TB as a second raidz2 vdev (12TB usable), throw out (or sell) the now unused 2x2TB left over

7) Add the 8x2TB raidz2 vdev to the pool with the 7x4TB raidz2 vdev (32TB usable)

8) At some point in the future, when I've run out of space again do an in-place upgrade of the 8x2TB to 8x4TB (or larger), giving me 44TB usable in total out of 60TB total (roughly three quarters usable space). With raidz1 this would be dangerous, because you have no redundancy when swapping out a disk, but with raidz2 this is safe, because you still have one parity disk while swapping a disk.

I'll lose a bit more capacity via this approach because I'll have dedicated 4 disks to parity instead of 3, but it means that any two of my disks can fail without causing me problems, and that I can do in-place upgrades without losing all redundancy, so that's worth it in the long run.

The problem with this process is it means my next upgrade step from right now is 7x4TB which is currently INSANELY EXPENSIVE.

EDIT: It should be noted that in-place upgrades with ZFS take forever, because it means you have to resilver (rebuild) your array one time per disk. So an 8x2TB -> 8x4TB upgrade would require 8 resilvers of the array, which would probably take weeks. But it's a raidz2, two drives of parity, so it's safe!
Developer: Tomato/MLPPP, Linux/MLPPP, etc »fixppp.org


Mississauga, ON

in your step 2,
you created 2 distinct pools right? i.e. pool1, and pool2?
which means after your done, your original Pool will now be gone and you'll be working with a new pool?

is there no way to do what you want with vdevs, to be able to keep the original pool?

Toronto, ON
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reply to Guspaz

said by Guspaz:

That's what friends are for.

I'm waiting for a 4TB Red to become available at or near $100 :P It will be a while, so I'm hoping my existing 10x2TB can last that long.

Are 4TB Reds coming out soon? I'd pull the trigger on 8x4TB of those for a new NAS setup... The hitachi 4TB's are too expensive and i'm looking to cut power usage from my fat server box to a more power efficient NAS.