ZFS in a VM?

krad kraduk at gmail.com
Wed Jun 3 08:58:28 UTC 2015

Strictly speaking its the online dedup that is expensive. Depending on your
data sets and work patterns you can dedup a pool by doing things
intelligently. eg use snap shots and clones where ever possible, if you
have any out of hour periods, turn dedup on and rewrite all new data on the
pool since the last dedup run (not a scrub). This is all getting off topic

On 29 May 2015 at 14:36, <kpneal at pobox.com> wrote:

> On Fri, May 29, 2015 at 07:26:01PM +1000, andrew clarke wrote:
> > On Wed 2015-05-27 13:31:05 UTC-0400, Jaime Kikpole (
> jkikpole at cairodurham.org) wrote:
> >
> > > Can I run a FreeBSD system in a virtual machine and use ZFS?  The VM
> > > environment is a commercial system based on Linux's KVM, if that
> > > matters.
> >
> > ZFS works better if it has "raw" access to the hard drive, in terms of
> > performance and error detection, but will still work fine without it.
> > Either way you'll still get all the usual features ZFS provides, such
> > as snapshots, dedup, compression, etc.
> Strictly speaking, error detection itself doesn't work better with raw
> disks. Error _correction_ works better with raw disks. Then again, this
> is what the "copies=2" or "copies=3" option is for: to be able to correct
> errors when ZFS is not handling the RAID or mirroring itself.
> > Keep in mind that large capacity ZFS datasets can require several GBs
> > of memory to work well, particularly if you're using dedup, so you'll
> > need to adjust your VM guest's memory appropriately.
> Be careful with dedup. The memory requirements are so large that with
> large amounts of data is is easy to get into a situation that takes days
> to recover from.
> When not using dedup: There are reports that ZFS can be used in as little
> as 4GB of memory -- in the i386 FreeBSD at that! I've got a small setup
> with 8GB of memory that works well for me, but I'm not using dedup until
> I can put a lot more memory in this machine.
> --
> "A method for inducing cats to exercise consists of directing a beam of
> invisible light produced by a hand-held laser apparatus onto the floor ...
> in the vicinity of the cat, then moving the laser ... in an irregular way
> fascinating to cats,..." -- US patent 5443036, "Method of exercising a cat"
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