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Date:      Sat, 30 May 2015 06:32:56 +1000
From:      andrew clarke <mail@ozzmosis.com>
To:        kpneal@pobox.com
Cc:        "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org>, Jaime Kikpole <jkikpole@cairodurham.org>
Subject:   Re: ZFS in a VM?
Message-ID:  <20150529203256.GA57654@ozzmosis.com>
In-Reply-To: <20150529133653.GA94981@neutralgood.org>
References:  <CA+sg5RQgF7+AQu9P0Bt8USF8722QCi=qJ2XQ8RbNQ92cv9tNTg@mail.gmail.com> <20150529092600.GA32731@ozzmosis.com> <20150529133653.GA94981@neutralgood.org>

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On Fri 2015-05-29 09:36:53 UTC-0400, kpneal@pobox.com (kpneal@pobox.com) wrote:

> > 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. 

I've used ZFS-on-root on amd64 with just 1.5 GB memory for a two-way 1 TB
mirror without any dramas for over a year. I wasn't using dedup or
snapshots, though, and I avoided running any userland software that
ate lots of memory. This was also on bare metal, not a VM.

It now has 4 GB, which is plenty.



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