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Date: Tue, 19 Oct 2010 12:49:15 +0100
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To: pjd@FreeBSD.org
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From: Pete French <petefrench@ticketswitch.com>
Cc: freebsd-fs@freebsd.org
Subject: Re: Converting a non-HAST ZFS pool to a HAST pool
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> Maybe I'm missing something, but how do you guys check this? Both
> gmirror and glabel use only single sector for its metadata, so 1kB in
> total. HAST metadata takes 4kB plus activemap size, which depends on
> provider size.

I checked it by disconnecting one half of the mirror - which
is on a separate machine in my case remember - and then setting
that machine up with hast. Created the hast device and did a 'diskinfo'
on the resulting device. Compared that to a 'diskinfo' on the original
provider.

Here are the results, for the bare disk, the hast device, the
mirrored device, and partition 'a' on the mirrored device. I
wrote a disklabel there when it was UFSA, in case you
were wondering.

diskinfo /dev/da0s1
/dev/da0s1      512     68718411776     134215648       0       16384   16447   255     32

diskinfo /dev/hast/serp0 
/dev/hast/serp0 512     68718403584     134215632       0       0

diskinfo /dev/mirror/mysql0
/dev/mirror/mysql0      512     68718410752     134215646       0       0

diskinfo /dev/mirror/mysql0a
/dev/mirror/mysql0a     512     68718402560     134215630       0       8192    8354    255     63

So my current zpool uses /dev/mirror/mysql0a which is 68718402560 bytes,
and when I move to hast I will be using /dev/hast/serp0 which is
68718403584 bytes - i.e. 1024 bytes larger. Note that if it wasn't
for the BSD style disklabel it would be larger, and wouldnt work.

-pete.