XigmaNAS

I read something that only 80% of the capacity of ZFS should be used and at least 20% should stay empty.

I use 2 different techniques with ZFS.

1. a ZFS-volume which is forwarded as an iSCSI-Target to my W2008R2 machine and used for Backup-to-disk.
2. a ZFS-dataset forwardes as a CIFS-share and also used as B2D on the W2008R2 machine.

Both seem to work after disabling the sync-feature.
But as more data is stored i am reaching the 80% margin for the ZFS-dataset.

Is this a problem ?

It might become a problem, please read here:
http://constantin.glez.de/blog/2010/04/ ... #freespace
and here
http://www.solarisinternals.com/wiki/in ... iderations

depends on the scenario.

if your writes are very infrequent and mostly reads then you can go higher than 80%.
ie just dumping large videos onto the pool. and then playing them.

however be warned. if your file system become completely full, you wont be able to delete files easily and need to do some command line trick to get around that.

The margins refer to the pool (zpool list), not any particular volume or dataset. Dataset have a limit usually equal to free space left on the pool, or a quota limit. You can fill a volume to whatever you think is appropriate for the type of filesystem you have on the volume, but keep in mind that many of those rules assume a real hard disk. ZFS doesn't work like a real hard disk.