RAID z2 -- 8 disks -- substantially less space than expected

[LightBulb]

Hi, I'm a first time FreeNAS user with a question about ZFS RAID z2.

Basic System info:
SuperMicro mobo
Xeon E5-1620
64 gig Registered ECC RAM

SSD for FeeNAS Operating System
6tb WD-RED x8 for storage

----
This is basically a home store & serve everything server.
---

I am hoping to maximize my storage with this server and have been perplexed
and a bit disheartened at the amount of storage I have avaliable under ZFS.

My understanding (probably very wrong) is that RAID z2 is somewhat equivalent to Raid 6.
I expected to lose 2 drives worth of storage. What I'm seeing is something different.

After attempting to create a single large 8-disk z2 array, I only see 20.5 terabytes available.
Under Storage > Volume Status I see what looks like two separate z2 arrays:

raidz2-1
disk 1
disk 2
disk 3
disk 4

raidz2-2
disk 1
disk 2
disk 3
disk 4

Did I make a mistake when attempting to create a single large z2 array (raid 6 equivalent)?
What did I end up creating? Is it a mirrored 4 disk array? Seems like a giant waste of disks
if that is the case. Perhaps I am misunderstanding how ZFS works.

I would like to recreate my array into a single 8-disk RAID z2 if this is possible.
If not I may opt for a z1 array (raid 5 equivalent-ish).

any pointers would be greatly appreciated.
thanks

 

[Spearfoot]

Hi, I'm a first time FreeNAS user with a question about ZFS RAID z2.

Basic System info:
SuperMicro mobo
Xeon E5-1620
64 gig Registered ECC RAM

SSD for FeeNAS Operating System
6tb WD-RED x8 for storage

----
This is basically a home store & serve everything server.
---

I am hoping to maximize my storage with this server and have been perplexed
and a bit disheartened at the amount of storage I have avaliable under ZFS.

My understanding (probably very wrong) is that RAID z2 is somewhat equivalent to Raid 6.
I expected to lose 2 drives worth of storage. What I'm seeing is something different.

After attempting to create a single large 8-disk z2 array, I only see 20.5 terabytes available.
Under Storage > Volume Status I see what looks like two separate z2 arrays:

raidz2-1
disk 1
disk 2
disk 3
disk 4

raidz2-2
disk 1
disk 2
disk 3
disk 4

Did I make a mistake when attempting to create a single large z2 array (raid 6 equivalent)?
What did I end up creating? Is it a mirrored 4 disk array? Seems like a giant waste of disks
if that is the case. Perhaps I am misunderstanding how ZFS works.

I would like to recreate my array into a single 8-disk RAID z2 if this is possible.
If not I may opt for a z1 array (raid 5 equivalent-ish).

any pointers would be greatly appreciated.
thanks

Looks like your pool is made up of a pair of striped 4-disk RAIDZ2 vdevs; half of your disks are being used for parity, which is wasteful of space and definitely not what you wanted.

You will have to destroy the pool and re-create it. Be sure to select all 8 disks and use RAIDZ2 for the 'Volume layout', as shown here:

 

[LightBulb]

okay, great news!
I'm not sure how I did what I did last time but I will be more careful this time and do as you suggest.

really appreciate the info.
cheers!

 

[Kevin Horton]

You got bit by the default behaviour of the GUI when creating a pool. If you have 8 disks, and select RAIDZ2, it unhelpfully draws a 4x2 grid of disk, which gives the setup you have. You need to manually grab the corner of the grid it drew, and make it a single line, 8 disks long, as shown by by @Spearfoot. That'll put all 8 disks in a single vdev.