After a few weeks using FreeNAS 8.3.1, I noticed I could not create new volumes because the pool was out of space. The problem was that I should have had enough space, by a long shot.
In fact, one of my “block” volumes was taking space more than twice it’s size. I had other volumes that seemed unaffected (or less affected), the only difference was that the problematic volume had volblocksize=8k set .
After a couple of days searching for answers, somebody else opened a support ticket for the exact same problem, but it was way worse than I thought. I only tested with volblocksize=8k and volblocksize=64k, but not all the other values. It appears that the smaller volblocksize, the more extra space is required, up to 23x the original space!
And more, the bug comes from FreeBSD 9 and is also present in FreeBSD 10 !
I’m going to reinstall this server with OpenIndiana (which is unaffected) as soon as possible because of this, a major bug like this shouldn’t have made it past beta…