RAIDZ2 6 disk, capcity only 1 disk?

[yashiharu]

i am testing FreeNAS on virtualbox
i created 6x 3GB harddisk

In the storage configuration in FreeNAS, for using all 6 disk, i got:
RaidZ1: 6 x 1 x 3.2GB = capacity 5 GB
RaidZ2: 6 x 1 x 3.2GB = capacity 4 GB
RaidZ3: 6 x 1 x 3.2GB = capacity 3 GB
Mirror: 6 x 1 x 3.2GB = capacity 1 GB
Stripe: 6 x 1 x 3.2GB = capacity 6 GB

I don't understand the way that FreeNAS calculated.
shouldn't a RaidZ2 with 6 3GB hard disk can get around 12GB capacity?

 

[danb35]

By default, FreeNAS takes 2 GB on each disk for swap. When you're using real drives, that amount is negligible, but when you're using small virtual disk files, it's much more noticeable.

 

[SweetAndLow]

When using it for testing in a virtual environment you can turn off the 2GB swap in the freenas settings.

 

[yashiharu]

thank you for all the reply.

i could have 32GB ram in real NAS.
Would it be better/faster to disable the swap on each drive??

 

[INCSlayer]

thank you for all the reply.

i could have 32GB ram in real NAS.
Would it be better/faster to disable the swap on each drive??

do NOT disable swap on the drives on a real machine

 

[Mirfster]

BTW, Bidule0hm created a nice "ZFS RAID size and reliability calculator" if you wanted to have a good way to estimate space:

Original Post:
https://forums.freenas.org/index.php?threads/zfs-raid-size-and-reliability-calculator.28191/

Direct Link:
http://biduleohm.free.fr/zfsraidsarc/

 

[SweetAndLow]

The swap isn't there to help with low memory situations. It's there to help with different disk sizes manufactures use.

 

[jgreco]

The swap isn't there to help with low memory situations. It's there to help with different disk sizes manufactures use.

Well, not entirely true. It's certainly there to help with one potentially catastrophic low memory situation: pool import of a dirty pool. In normal operation swap shouldn't be touched, if it is, you don't have enough RAM.