Date: Sat, 25 Feb 2012 10:04:02 +0100 From: Peter Maloney <peter.maloney@brockmann-consult.de> To: freebsd-fs@freebsd.org Subject: Re: glabel, gpart and zfs confusion. Message-ID: <4F48A402.70009@brockmann-consult.de> In-Reply-To: <3E3E4094-77E2-490B-9574-5B95ECDED447@pean.org> References: <3E3E4094-77E2-490B-9574-5B95ECDED447@pean.org>
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In Solaris, I've read that the IO system is designed such that a some
commands (eg. flush of a partition) does not necessarily flush the
disk's write cache... like the command can't move up the chain. So if
you put zfs on a partition, you can get data loss (eg. transaction
rollback required and probably no corruption).
In FreeBSD, things are different I am told, without the above
limitation. So you can happily put zfs on partitions, and the zfs code
can keep your data safe. I haven't had data loss with system panics
during sync writes with my ZIL on a partition, so I guess this must be true.
People say that glabel is buggy/a hack. But I haven't had any problems
myself. So they suggest using gpt to label your disks. I find that
sometimes your gpt labels get eaten though, and you end up with gptid in
your zpool status output. For labels to get eaten, you need to import
the pool elsewhere with -f usually. And maybe this only applies to the
root pool in most cases (but I definitely had one other case when it
happened to a different pool). There is something you can add to
/boot/loader.conf to get rid of the gptids... but I am hesitant to use
it... because what happens when you have 2 identical labels and gptid is
gone?
eg.
NAME STATE READ
WRITE CKSUM
zroot DEGRADED
0 0 0
mirror-0 DEGRADED
0 0 0
gptid/bcc6c93a-f332-11e0-a5b6-0025900edbca OFFLINE
0 0 0
gptid/4629fb4b-f596-11e0-a5b6-0025900edbca OFFLINE
0 0 0
gpt/root2 ONLINE
0 0 0
gpt/root3 ONLINE
0 0 0
And also if a whole disk goes bad, and you try to replace it with
another whole disk that is 1 byte smaller, it won't allow you to do
that. So if you use gpart and create a slightly smaller partition, you
get the advantage of being able to replace disks with smaller ones later.
For new systems, I am using gpt labels. And if the gptid thing appears,
I just ignore it.
Am 25.02.2012 09:42, schrieb Peter Ankerstål:
> Hi,
>
> Now Im really confused.
>
> I want in some way label my drives so the setup is independent of physical setup. But Jason doesn't
> seem to like glabel at all. :D
> http://lists.freebsd.org/pipermail/freebsd-fs/2012-January/013574.html
>
> And then he says that you should use gpart instead
> http://lists.freebsd.org/pipermail/freebsd-fs/2012-January/013578.html
>
> But this seems to be in conflict with the common knowledge that zfs should
> be used on whole disks, not partitions!
>
> Any pointers?
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