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? > _______________________________________________ > freebsd-fs@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org"
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