Date: Thu, 22 Jul 2010 08:49:42 -0400 From: Paul Mather <paul@gromit.dlib.vt.edu> To: Dan Langille <dan@langille.org> Cc: freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: Using GTP and glabel for ZFS arrays Message-ID: <5A35E293-87C2-4E96-863F-1734B2ECA796@gromit.dlib.vt.edu> In-Reply-To: <4C47B57F.5020309@langille.org> References: <4C47B57F.5020309@langille.org>
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On Jul 21, 2010, at 11:05 PM, Dan Langille wrote: > I hope my terminology is correct.... >=20 > I have a ZFS array which uses raw devices. I'd rather it use glabel = and supply the GEOM devices to ZFS instead. In addition, I'll also = partition the HDD to avoid using the entire HDD: leave a little bit of = space at the start and end. >=20 > Why use glabel? >=20 > * So ZFS can find and use the correct HDD should the HDD device ever > get renumbered for whatever reason. e.g. /dev/da0 becomes /dev/da6 > when you move it to another controller. I have created ZFS pools using this strategy. However, about a year ago = I still fell foul of the drive shuffling problem, when GEOM labels = appeared not to be detected properly: = http://lists.freebsd.org/pipermail/freebsd-geom/2009-July/003654.html This was using RELENG_7, and the problem was provoked by external USB = drives. The same issue might not occur with FreeBSD 8.x, but I thought I'd point = out my experience as a possible warning about using glabel. Nowadays, I use GPT labels ("gpart ... -l somelabel", referenced via = /dev/gpt/somelabel). > Why use partitions? >=20 > * Primarily: two HDD of a given size, say 2TB, do not always provide > the same amount of available space. If you use a slightly smaller > partition instead of the entire physical HDD, you're much more > likely to have a happier experience when it comes time to replace an > HDD. >=20 > * There seems to be a consensus amongst some that leaving the start = and > and of your HDD empty. Give the rest to ZFS. You should also try and accommodate 4K sector size drives these days. = Apparently, the performance boosts from hitting 4K-aligned sectors can = be very good. Cheers, Paul.=
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