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Date: Sun, 27 Jan 2013 10:02:57 +0100
From: Adam Nowacki <nowakpl@platinum.linux.pl>
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To: freebsd-fs@freebsd.org
Subject: Re: ZFS slackspace, grepping it for data
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On 2013-01-27 09:36, grarpamp wrote:
> Say there's a 100GB zpool over a single vdev (one drive).
> It's got a few datasets carved out of it.
> How best to stroll through only the 10GB of slackspace
> (aka: df 'Avail') that is present?
> I tried making a zvol out of it but only got 10mb of zeros,
> which makes sense because zfs isn't managing anything
> written there in that empty zvol yet.
> I could troll the entire drive, but that's 10x the data and
> I don't really want the current 90gb of data in the results.
> There is zdb -R, but I don't know the offsets of the slack,
> unless they are somehow tied to the pathname hierarchy.
> Any ideas?

zdb -mmm pool_name
for on-disk offset add 0x400000 If i remember correctly.