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 offsetfstype [fsize bsize bps/cpg] a: 629145604.2BSD 2048 16384 28552 b: 4194304 6291456 swap c: 4883920020unused0 0 # raw part, don't edit d: 41943040 104857604.2BSD 2048 16384 28552 e: 2097152 524288004.2BSD 2048 16384 28552 f: 31457280 545259524.2BSD 2048 16384 28552 g: 31457280 859832324.2BSD 2048 16384 28552 h: 370951490 1174405124.2BSD 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 [EMAIL PROTECTED] ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: 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 offsetfstype [fsize bsize bps/cpg] a: 629145604.2BSD 2048 16384 28552 b: 4194304 6291456 swap c: 4883920020unused0 0 # raw part, don't edit d: 41943040 104857604.2BSD 2048 16384 28552 e: 2097152 524288004.2BSD 2048 16384 28552 f: 31457280 545259524.2BSD 2048 16384 28552 g: 31457280 859832324.2BSD 2048 16384 28552 h: 370951490 1174405124.2BSD 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 [EMAIL PROTECTED] FreeBSD committer pgpwOyU1JUUd2.pgp Description: PGP signature
Re: gmirror is confusing me, will I be bitten by the last-sector-use?
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. So long as your partition(s) exist(s) within the mirror device, you can't problem the metadata. If you tried writing to the last sectors of /dev/ad0 or /dev/ad2, you would damage or destroy the metadata. So, don't do that. I am curious about this case, does FreeBSD periodically check for the existance of the metadata, or (like some things, the kernel for instance) does it, once read and not rewritten, exist in memory, thus being able to be written over on disk, not to be noticed until reboot (or modification, if such would be your wont)? -- -- ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to [EMAIL PROTECTED]
