Have 4 disks but unable to create RAIDZ2 config

[highbury]

Hi,

I have a HP MicroServer with 4 x 3TB disks and 8GB memory, when trying to create my first volume, I'm only given the option to configure a mirrored set and not a RAIDZ2 config.

This is what results if I build what the 9.1 installer allows

[root@freenas] ~# zpool status -v
pool: ILSLEY-DATA1
state: ONLINE
scan: none requested
config:

NAME STATE READ WRITE CKSUM
ILSLEY-DATA1 ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
gptid/a87393dd-076a-11e3-9c82-68b59972b169 ONLINE 0 0 0
gptid/a9215319-076a-11e3-9c82-68b59972b169 ONLINE 0 0 0
mirror-1 ONLINE 0 0 0
gptid/a9d3a943-076a-11e3-9c82-68b59972b169 ONLINE 0 0 0
gptid/aa8077dd-076a-11e3-9c82-68b59972b169 ONLINE 0 0 0

errors: No known data errors
(apologies if this doesn't display in fixed pitch)

I've destroyed this volume, thinking I missed an option on setup, but the Volume Layout option on the ZFS Volume Manager, only offers me the choice of "Mirrored, Stripe, Log or Spare"
How can I configure my system with RAIDZ2 ?
Thanks

 

[N00b]

Hi, What version of FreeNAS are you on? In version 9.x.x you see a slider that will allow you to select the no of disks. Then the drop down will allow you to select the type of config (RAIDZ, RAIDZ1 etc). If you don't select the disks then you don't get the drop down choices. Does this work for you?

 

[highbury]

I'm running 9.1. Interesting UI, but doing it the way you suggested worked

What I did was work down the screen, and first click on the + by the available disks to add the disks into the volume, that moved the disks into the Volume layout section in a 2+2 mirrored layout, where the pull-down volume type option didn't show RAIDZ2. Of course I didn't realise I could have dragged the little circle slider up and along to make a single row, and voilà I now see a volume type of RAIDZ2.

As a suggestion, maybe allow people to set the volume type to whatever is possible given the number of disks they have, and use that to drive the volume layout, rather than rely solely on using the little circular slider/puck to control everything?

Many Thanks

 

[highbury]

As a quick follow-up question - how much data should I expect to see with a RAIDZ2 config consisting of 4 x 3TB disks? I'm currently seeing 5.2TiB, after creating my vdev, but before creating my zpool, I was hoping for nearer to 8.

 

[gpsguy]

Why would you think you'd get 8Tb with 4x3 in RAIDz2? With 2 parity drives, simple math would say the number is less than 6Tb. Unfortunately, the drive manufacturers use a different calculation than the OS's. A 2Tb drive only has about 1.8Tb of usable space.

 

[highbury]

Thanks for your reply, yes I forgot RAIDz2 now uses 2 parity disk, so the best I'll ever get is 6GB - disk manufacturer maths tax - formatting, i.e 5.2TiB

Interesting Ref: http://dtrace.org/blogs/ahl/2006/06/18/double-parity-raid-z/