Storage question

Matthew Seaman m.seaman at
Wed Sep 9 15:52:04 UTC 2015

On 2015/09/09 16:15, William A. Mahaffey III wrote:
> I have heard that filling your zpool is a *BAD* thing, but it can be for
> any FS, just maybe a bit worse for ZFS. I am going to study that option
> a bit more. The online docs all seem to show swap within the zpool as
> well, does that work OK, performance wise ? It would simplify
> installation, however I am planning to script that, so a bit of 'extra'
> effort for separate swap partitions is not an issue. I have always
> thought that separate swap partitions directly kernel managed were the
> best for swap performance if/when it gets down to that, no ?

Filling the zpool completely is tricky because it can be hard to
recover.  The trick is (a) don't do that; (b) create space by
*truncating* a large file if it happens.  Or use FreeBSD 10.x which has
a 3% space reservation, similarly to how UFS does.

However, you'll find that ZFS performance drops quite a bit when you hit
somewhere north of about 75% full.

Yes, you should swap to a dedicated partition, rather than swapping
within ZFS.  I think, BICBW, that you can still get into a deadlock
where you need extra memory to handle an out-of-memory condition.

Just use the system installer to set up your drives and zpool -- it
makes it ridiculously easy.



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