Bad sizing of available space on ZFS volume

[awaz]

Hello,

My configuration is
Freenas i386 v8.0.1.RC2
Motherboard ASUS P7H55-M/USB3
CPU Intel Core i3 550
Corsair 8 Gb RAM, 4 Gb used, upper 4Gb ignored
Freenas SW running on 16Gb Patriot XT Rage USB key
4 SATA II disks : 2 x 2T, 2 x 1T

One only volume is defined enclosing the 4 SATA disks, configured ZFS and mirroring.
In that configuration I was expecting to get 3T available disk space. Only 1T is seen available. All attempts to allocate datasets leading to needs space available above the 1T are rejected.
Is there any explanation and hint to overcome this issue ?
Thanks a lot for your help.
Kind regards
Albert

PS : displaying volume disks shows that the 4 disks are taken into account in volume configuration

 

[joeschmuck]

Albert,
Be specific and pretend we cannot see your screen. How exactly did you set up the hard drives? Which ones are of what type of RaidZ and/or mirroring? For example I have four 2TB drives all configured as a single RAIDZ which gives me ~6TB of data storage. I could have arranged these drives as: four drives all configured as a single RAIDZ2.

Also, if you mix drive sizes in a RAIDZ, the smallest drive size is what all the drives in that pool will represent. It's a ZFS thing.

-Mark

 

[awaz]

Thanks Mark for your quick answer and sorry if apparently, I was not enough clear.

My disk configuration was declared as such :
I activated creation of the volume,
I added the 4 disks to the volume, so 6 TB (2 x 2TB + 2 x 1TB),
I flagged mirror button.
I created the volume.

When displaying disks of the declared volumed, it is confirmed that the 4 disks are members of the volume in mirror mode.

My intention is to use mirroring for the 6TB so giving 3TB available space. I don't want to use RAIDZ nor RAIDZ2 configurations. Full mirroring only.

I hope it helps
kr
albert

 

[joeschmuck]

So you set up a 4 disk mirror and it will mirror only the smallest size so that is why you have 1TB. I understand what you want but not sure you can do that as a single volume. You can create two mirrored volumes, 2x2 in Volume1, and 1x1 in Volume2. But it's two separate drive mirrors. There are people here that are good with this type of stuff somewhere on the forums.

-Mark

 

[awaz]

Thanks Mark.

It looks really very questionnable if capacity of mirrored volume is limited to the capacity of the smaller disk, whatever the number of disks of the volume. This is one of the most important functionality brought by ZFS to allow high capacity volumes and extensions by adding disks when needed !

I have some reluctance in believing it (except if it is a limitation of current implementation, which I could understand):

As proposed by Mark, may some ZFS domain expert from the forum provide confirmation, explanation or solution ?

Thanks and br

albert

 

[awaz]

Me again.

I found out the solution in the documentation.
Extract :
"The volume creation screen allows for advanced scenarios:
to create a mirror (RAID 1): check the 2 disks to go into the mirror from the list of available disks
to create a striped mirror (RAID 10): create 2 mirrors with the same volume name"

I tried it and it's OK.
Point closed.
kr
albert

 

[joeschmuck]

I know I'd heard how to do it once but since I have never done that specifically I felt uncomfortable giving advice. Glad you got it working the way you wanted.

-Mark

 

[awaz]

Thanks Mark for your kind attention.
br
albert