Eivind Olsen
2006-Feb-21 01:58 UTC
gmirror is confusing me, will I be bitten by the last-sector-use?
Hello. I've just configured a server to use gmirror (using FreeBSD 6.1b2). I followed the tutorial on http://www.onlamp.com/pub/a/bsd/2005/11/10/FreeBSD_Basics.html and did it install-time. Then I read in the gmirror(8) man-page that gmirror uses the last sector of the provider to store metadata. My mirror consists of two IDE-disks/consumers (ad0 and ad3), both showing a mediasize of "250059350016 (233G)" in "gmirror list". The provider is shown as having a mediasize of 250059349504. Sectorsize = 512. Now, how can I check whether my current partitions will cause trouble with the metadata-sector or not? I've done some searching on the net, but I'm still a bit confused. If I understand correctly, the consumers ad0/ad2 span 488397168 sectors (mediasize/sectorsize), and the mirror/gm0 spans 488397167 sectors. Here's the output from bsdlabel: vimes# bsdlabel /dev/mirror/gm0s1 # /dev/mirror/gm0s1: 8 partitions: # size offset fstype [fsize bsize bps/cpg] a: 6291456 0 4.2BSD 2048 16384 28552 b: 4194304 6291456 swap c: 488392002 0 unused 0 0 # "raw" part, don't edit d: 41943040 10485760 4.2BSD 2048 16384 28552 e: 2097152 52428800 4.2BSD 2048 16384 28552 f: 31457280 54525952 4.2BSD 2048 16384 28552 g: 31457280 85983232 4.2BSD 2048 16384 28552 h: 370951490 117440512 4.2BSD 2048 16384 28552 So, the "h" partition, which is the last one, has offset=117440512 and size=370951490, and if I add those together I get 488392002. Does this mean that my "h" partition ends at 488392001 (right before 488392002), and I'm still several sectors away from the metadata? Or am I misunderstanding things here? -- Regards / Hilsen Eivind Olsen <eivind@aminor.no>
Ruslan Ermilov
2006-Feb-21 04:14 UTC
gmirror is confusing me, will I be bitten by the last-sector-use?
On Tue, Feb 21, 2006 at 10:58:30AM +0100, Eivind Olsen wrote:> Hello. > > I've just configured a server to use gmirror (using FreeBSD 6.1b2). I > followed the tutorial on > http://www.onlamp.com/pub/a/bsd/2005/11/10/FreeBSD_Basics.html and did > it install-time. > Then I read in the gmirror(8) man-page that gmirror uses the last sector > of the provider to store metadata. > > My mirror consists of two IDE-disks/consumers (ad0 and ad3), both > showing a mediasize of "250059350016 (233G)" in "gmirror list". The > provider is shown as having a mediasize of 250059349504. Sectorsize = 512. > > Now, how can I check whether my current partitions will cause trouble > with the metadata-sector or not? I've done some searching on the net, > but I'm still a bit confused. If I understand correctly, the consumers > ad0/ad2 span 488397168 sectors (mediasize/sectorsize), and the > mirror/gm0 spans 488397167 sectors. >In short: kernel (g_mirror) won't let you write to the last sector of its media.> Here's the output from bsdlabel: > > vimes# bsdlabel /dev/mirror/gm0s1 > # /dev/mirror/gm0s1: > 8 partitions: > # size offset fstype [fsize bsize bps/cpg] > a: 6291456 0 4.2BSD 2048 16384 28552 > b: 4194304 6291456 swap > c: 488392002 0 unused 0 0 # "raw" part, > don't edit > d: 41943040 10485760 4.2BSD 2048 16384 28552 > e: 2097152 52428800 4.2BSD 2048 16384 28552 > f: 31457280 54525952 4.2BSD 2048 16384 28552 > g: 31457280 85983232 4.2BSD 2048 16384 28552 > h: 370951490 117440512 4.2BSD 2048 16384 28552 > > So, the "h" partition, which is the last one, has offset=117440512 and > size=370951490, and if I add those together I get 488392002. Does this > mean that my "h" partition ends at 488392001 (right before 488392002), > and I'm still several sectors away from the metadata? Or am I > misunderstanding things here? >Your "c" partition (the whole disk) occupies 488392002 sectors. The "h"'s partition last sector is 117440512+370951490-1=488392001. Cheers, -- Ruslan Ermilov ru@FreeBSD.org FreeBSD committer -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 187 bytes Desc: not available Url : http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20060221/23df1191/attachment.bin