Why is my volume showing less space than one would expect for the number of disks

[bra1n]

I created a volume as a RAIDZ1 with 6, 4TB disks. My understanding is that this would have created a volume with ~20TB of free space, but when viewing the volume it shows only 16.8 TB available. I expect that I'm either missing something obvious or that I'm misunderstanding how FreeNAS reports free space. This is my first time creating a volume that wasn't just a straight mirror.

Thanks in advance for your help.

 

[Bidule0hm]

No, it shows 16.8 TiB, it's not the same as 16.8 TB (1 TB = 0.909 TiB).

Also, there's some overhead taken by ZFS, it's normal ;)

NB: it's not recommended to use RAID-Z1 with drives bigger than 1 TB, see the "RAID-Z1/RAID5 isn't recommended" link in my signature.

 

[bra1n]

AHA. I see. I found a TiB to TB calculator and that and the ZFS overhead makes sense. I'm going to rebuild the zpool as a RAIDZ2 after some reading I did. There is nothing on the volume now so nothing of value will be lost ;)

Thanks!

 

[DrKK]

I concur, with 4TB drives, particularly 6 of them, I would suggest RAID-Z2, and I am the most forgiving of the guys on here in terms of RAID levels. So if *I* am saying RAID-Z2, you can bet you better use RAID-Z2.

:)

 

[satyr]

I wanted to bump this thread with a similar question. Taking into account overhead and drive space, here's what I'm left with. FWIW, I'm running 6x5TB drives in a RAID-Z2 config. Does this amount of available space seem appropriate? The volume's size seems about right (~27.3 TiB is roughly accurate for 30 TB advertised size). And the 8 TiB difference between the volume and primary dataset should be the 2 parity drives, correct?

 

[depasseg]

Look up 3 posts from your to Bidule0hm's post. He has a calculator in his signature. Come on man.

 

[Bidule0hm]

The total space is 27.3 TiB which is right (27.28 calculated).

The data usable space is 17.6 TiB which is right too (17.90 calculated but I've not implemented all the overheads).

 

[satyr]

Look up 3 posts from your to Bidule0hm's post. He has a calculator in his signature. Come on man.

I did use the calculator. I was merely making sure that the difference between the volume and primary dataset is the parity drive.

The total space is 27.3 TiB which is right (27.28 calculated).

The data usable space is 17.6 TiB which is right too (17.90 calculated but I've not implemented all the overheads).

Thanks for the clarification!

 

[Bidule0hm]

the difference between the volume and primary dataset is the parity drive.

Yes it is ;)