Why does Truenas "claim" 200GiB of a 1.8TiB pool?

[Casvt]

Hey there,

I have two 2TB drives in a mirror on my TrueNas Core system. Everything is working fine but recently I noticed something: I only have 1.6TiB of available space. The drives are 2TB so that is 1.82TiB. That means that TrueNas takes 200GiB of space in order for the mirror to work. It's the most simple mirror setup possible: two drives in a mirror vdev and that's all. Ofcourse there are snapshots taken of some sub-datasets but they are 'put' in the 1.6TiB space. So that means that TrueNas is taking 200GiB of space purely for the functionality of the mirror.

200GiB?? Why does it need so much? Why does TrueNas need 200GiB of space for the most simple mirror to work?

Again, everything is working fine. I'm just curious where all that space is going to.

Thanks in advance.

 

[Alecmascot]

This comes up all the time .
Search for "disk space"

ZFS Capacity Calculator - WintelGuy.com

ZFS / RAIDZ Capacity Calculator - evaluets performance of different RAIDZ types and configurations

wintelguy.com

 

[Casvt]

This comes up all the time .
Search for "disk space"

ZFS Capacity Calculator - WintelGuy.com

ZFS / RAIDZ Capacity Calculator - evaluets performance of different RAIDZ types and configurations

wintelguy.com

Yeah I know. I'm fine with zfs taking up the space; I'm just curious for what that 200GiB is needed. I'm asking for a wikipedia link that explains it basically. Just trying to learn a bit more about ZFS and how it works. That's all.

 

[artlessknave]

that's basically the metadata. pointers to the files, checksums of the files, checksums of the checksums, parity of the files, checksums of the parity of the files, duplicates of the metadata, pool info, vdev info, etc, etc.
think of it like a physical file cabinet, where the folders and dividers take up physical space, sometimes more than the documents if there are a lot of divisions.

all filesystems take up some space on a disk, but ZFS is quite a bit more than just a file system, doing volume manager, filesystem, and disk check all one.

 

[Alecmascot]

Yeah I know. I'm fine with zfs taking up the space; I'm just curious for what that 200GiB is needed. I'm asking for a wikipedia link that explains it basically. Just trying to learn a bit more about ZFS and how it works. That's all.

I am sure that with the search tools available to us all that you can find the information that you seek

 

[joeschmuck]

I am sure that with the search tools available to us all that you can find the information that you seek

I agree, this topic comes up all the time and it's been published here on the forums quite a bit. Most things can be found by doing a Google search for "truenas" and then your problem/question. It may take a few minutes, or 30 to read through the results but I'm sure they are there. That is how I look for answers to my questions all the time. I won't say that the forum search tools are fantastic but sometimes they work too.