RaidZ2 and simulation, what size is really usable ?

[iXô]

Hello,

waiting my hardware to be shipped, I am using a virtual machine to do some tests (KVM is the host).

I have declared 7 discs, each of 3GB. The first one is for the system, the 6 others are for a raid-z2 volume.

I have created the raid-z2 volume with the web gui, and it gives me this :

I don't really understand, what is really available to use ? (I am a total noob with zfs, but want to learn).

When I am using the calculator here : http://www.servethehome.com/raid-calculator/

It gives me this :

But using this calculator : https://jsfiddle.net/Biduleohm/hfqdpbLm/10/embedded/result/

I have this (using TB or GB can change something ?)

When enabling share on the root of the volume (/mnt/vol1) I found to be abble to use 4.13GB (some 1000/1024 magic here ?)


So can someone tells me what are the 2 sizes in the storage view (6 and 3.9) and what is really usable ?


Thanks for any help.

PS : disk list :

 

[Bidule0hm]

The STH calculator gives you the raw data usable space (without the overheads and the 80% rule). Mine gives you the same on the Total data space line and the real usable space (about 9.5 GB) after the overheads (they are not finished yet, the blocks overhead and allocation overhead aren't present for now) and the 80% rule. The GiB values are a bit off (by a few percents) because the GB --> GiB ratio isn't the same that the TB --> TiB ratio.

From what I can see you've not used 3 GB drives but 3 GiB drives (that's why the 3.2 GB in the drives list).

There is 2 GiB (or GB, don't remember) of swap per drive by default so with 3 GiB drives you can use only 1 GiB on them.

The storage tab gives you the free total RAID space on the root dataseet (6 GiB, 6x 1 GiB) and the free usable data space on the other dataset (3.9 GiB, 4x 1 GiB minus the overheads). If you want the total usable space just add the used and available values (but for now your pool is empty so the used space is roughly zero) ;)

 

[iXô]

Ok ! So the 'lost' space was the swap per drive because of the test on really small drives, in fact it also explain why I was unable to create the volume with 1GB drives !

Thanks for you answer.

 

[Bidule0hm]

Yeah, exactly ;)

You're welcome :)

 

[cyberjock]

This is all explained in the FreeNAS manual if you read the section on testing FreeNAS in a VM. ;)