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Date:      Mon, 10 Aug 2015 10:42:06 +0200
From:      Willem Jan Withagen <wjw@digiware.nl>
To:        Da Rock <freebsd-fs@herveybayaustralia.com.au>, freebsd-fs@freebsd.org
Subject:   Re: Urgently need some help solving lost space due to snapshots during receive op
Message-ID:  <55C863DE.3000200@digiware.nl>
In-Reply-To: <55C82BCD.2050404@herveybayaustralia.com.au>
References:  <55C82BCD.2050404@herveybayaustralia.com.au>

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On 10-8-2015 06:42, Da Rock wrote:
> I'm trying to move a pool from one system to another - exact same hdd
> and config, different in other areas. Both register same space
> available, and so should be no issue. The old system is quite full -
> still at least 5% free though.

Hi,

Are the versions of your FreeBSD also equal?

Because in newer version, the free space reservation is significantly
bigger. So if disks are equal size, then with newer FreeBSDs you have
less usable space available.
Don't know the exact SVN commit where it happened. But there are more
question on this topic in the list, and they all boil down to the same
thing: ZFS needs more reserved space to be able to do certain things
without freezing the system.

I've not read any suggestions that you can circumvent this setting.

As a second note I think is is more or less general understanding that a
ZFS systeem needs a lot more space left free than 5% to actual be able
to perform.
Last number I remember as sensible maximum fill level is around 70%.
If you go over it, your system is going to be busy with ZFS bookkeeping
instead of data storage.
(One of the things I remember from the ZFS lecture by Kirk McKusik,
which I no longer can find on YouTube :( )

--WjW

> I have done a recursive snapshot on the system and a send/receive over
> ssh. Near the end, it final croaks and says no space left. The snapshot
> it is sending is nowhere to be found on the receiving system.
> 
> Ok, checked free space - should be enough - so I try a simple cp op on
> the last dataset, but then it again croaks no space near the end, but at
> least I have some data.
> 
> Checking space again, it says free space of an expected value, but still
> won't allow further data.
> 
> I can't seem to figure out why this is not working, I'm currently trying
> using compression on the dataset to see if it can't squeeze it on there,
> but I still have a couple of no space messages so far.
> 
> Where has my space gone?!
> 
> TIA
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