Preliminary disk planning, am I wrapping my head around this correctly?

[JTheNASBuilder]

I've been doing a lot of reading about ZFS, FreeNAS, and the pro/con of various drive configurations. A lot of my early planning hinges simply on selecting hardware, making sure I have a case that can accommodate all the disks I want/need, etc. With that in mind, does this seem like a reasonable growth plan?

• • Phase 1:
    • Set up a RaidZ3 (5x1TB) for family photos (and critical documents)
    • Set up a RaidZ2 (6x3TB) for media (movies, tv shows, etc.)
  • Phase 2:
    • Set up additional RaidZ2 pools as my storage needs grow.

Am I being overly cautious? Would it make more sense to go with a bigger initial RaidZ2 pool and forget about the Z3 altogether? It's not like I don't back up all those photos and documents to external media as well as cloud-based services... and it's not like the data changes a lot or is part of the critical infrastructure of a company.

On a related note... I've been playing with ZFS raid pool calculators online and it seems like your overhead desceases significantly as you build a larger pool. (e.g. a 4 x 4TB Z2 array is 50% overhead but a 12 x 4TB array is like 23% overhead). What's the story there? How risky is it to build a bigger pool with numerous disks?

 

[Michael Wulff Nielsen]

It's not that risky. Personally I have a 6x3TB Raidz2 pool. That gives me 2 parity disks and 4 storage disks.

With your setup you would have 2TB + 12TB of space, with 3TB + 6TB of parity data. You are paying a lot for parity in that setup.

If you build a single zpool with 7*3TB in raidz2 you would have 15TB of available space with 6TB of parity data. And you can loose 2 drives and still resilver correctly.

I know that it is not the magic number of drives, but for a home installation it will perform well enough. So for a home installation I would go with a single vdev in raidz2, and add an ups to my setup.

 

[indy]

I feel raidz2 + backup is a good protection strategy for home users.

For a statistical analysis of different configurations you can take a look at:
http://www.servethehome.com/raid-calculator/raid-reliability-calculator-simple-mttdl-model/

 

[JTheNASBuilder]

You guys have persuaded me that I might have been planning a bit too hardcore for a home server setup... so Raidz2 + my regular backup routine it is.

If I'm going with Raidz2 and I'm planning on buying my disks in waves (as oppose to, you know, dropping $2000+ on hard drives all at once) what would you recommend as a balance between number of hard drives, parity overhead, and expense? As I mentioned above, I noticed significant decreases in parity overhead when increasing the total number of disks. Is there any risk to that? Is it that ZFS is really efficient or is it that Z2-based pools get more risky as you pack in more disks?

 

[Michael Wulff Nielsen]

The problem with building a FreeNAS system with ZFS is that you need to drop in the disks at once. So if you have zpool with a single zdev in raidz2 you need all the disk to create it. You can't create a zdev and add disks later.

So for every zdev in your pool you have to pay the parity costs, which basically means buy all the drives at once. But I feel your pain since I dropped almost $1000 on 6 disks.

 

[JTheNASBuilder]

Yeah =/

My original plan was to buy the disks in sets of 4... 4TBx4, then 4TBx4, etc. But after just two iterations of that plan, I'd already have lost around 16TB to parity, where as just saving a little longer and switching to 4TBx8 drops my overhead down around 10TB (so it's like getting two of those expensive 4TB disks for "free" as it were).

At present prices that changes my disk startup cost from around $700 to around $1400 if I were to stick with 4TB disks.

 

[tio]

It's not that risky. Personally I have a 6x3TB Raidz2 pool. That gives me 2 parity disks and 4 storage disks.

With your setup you would have 2TB + 12TB of space, with 3TB + 6TB of parity data. You are paying a lot for parity in that setup.

If you build a single zpool with 7*3TB in raidz2 you would have 15TB of available space with 6TB of parity data. And you can loose 2 drives and still resilver correctly.

I know that it is not the magic number of drives, but for a home installation it will perform well enough. So for a home installation I would go with a single vdev in raidz2, and add an ups to my setup.

If he loses 2 drives and goes to resilver he will very likely lose the pool due to the high likelihood of a URE on the remaining drives due to the high capacity.

For home setup theres nothing wrong with doing a 6 drive 3TB RZ2 and keeping a spare on hand just in case one fails. Create one Zdev and then just create datasets for the uses you planned which simplifies the whole process massively.