Disk space confusion

[Lordadmiral Drake]

My FreeNAS box currently has a single 1TB drive for data storage.
On the Webinterface it states total disk space as 914GiB (which is normal).
But one thing strikes my eye: While I currently have about 710GiB of Data on this drive there is only about 100GiB of free space left, so 100GiB are missing (free and used space numbers also from Webinterface).
Whats causing this discrepancy?

 

[ZFS Noob]

How much is reserved? ZFS is copy-on-write, so running out of space is a really bad thing, and some space is reserved by default.

 

[Lordadmiral Drake]

Oh, I forgot to mention, the drive is UFS formatted as my hardware is insufficient for ZFS

 

[ZFS Noob]

You've got me, then.

 

[Dusan]

How much is reserved? ZFS is copy-on-write, so running out of space is a really bad thing, and some space is reserved by default.

Are you sure? I never saw ZFS do that. In fact, it will happily let you completely fill a pool, to the point of rm failing due to the COW nature of the filesystem (there is no empty block to store the new copy of the directory).

Oh, I forgot to mention, the drive is UFS formatted as my hardware is insufficient for ZFS

On the other hand, UFS does exactly that -- by default it reserves 8% of the disk capacity. You can check the minimum percentage of free space by running "tunefs -p <filesystem>". For more details see the description of the -m option here: http://www.freebsd.org/cgi/man.cgi?query=tunefs

 

[ZFS Noob]

Are you sure? I never saw ZFS do that. In fact, it will happily let you completely fill a pool, to the point of rm failing due to the COW nature of the filesystem (there is no empty block to store the new copy of the directory).

On the other hand, UFS does exactly that -- by default it reserves 8% of the disk capacity. You can check the minimum percentage of free space by running "tunefs -p <filesystem>". For more details see the description of the -m option here: http://www.freebsd.org/cgi/man.cgi?query=tunefs

And there you go. :)

(I was thinking about the volume reserved space field you fill out when creating a pool.)