Understanding LVM UUIDS
in [Debian]
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From: Alan Chandler on 23 Jun 2010 13:40 On 23/06/10 11:20, Javier Barroso wrote: > On Wed, Jun 23, 2010 at 10:40 AM, Alan Chandler > <alan(a)chandlerfamily.org.uk <mailto:alan(a)chandlerfamily.org.uk>> wrote: > > I feel I should move my entire /etc/fstab over to using uuids > .... > Get your uuid from dumpe2fs -h /dev/vg/lv | grep UUID > > But /dev/vg/lv is a persistent name, so no sense changing it to uuid, or > maybe I'm missing something ? > My brain fade - of course I can use the persistent name -- Alan Chandler http://www.chandlerfamily.org.uk -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/4C224433.2070400(a)chandlerfamily.org.uk
From: Aaron Toponce on 23 Jun 2010 15:10 On 06/23/2010 09:47 AM, Camaleón wrote: > On Wed, 23 Jun 2010 09:40:22 +0100, Alan Chandler wrote: >> I feel I should move my entire /etc/fstab over to using uuids > > Mmm... any strong reason for doing that? :-) Whether or not these are his reasons, I can tell you why that is a wise move. UUIDs are unique to the device/filesystem. The major advantage of using UUIDs is that you don't have to worry about reordering of disks by the kernel when it sees it in a different order than previous. > I'm with Lenny and the old naming method ("/dev/sdx") is the default for > "/etc/fstab". This isn't recommended, because if the Linux kernel developers change drivers, and the drives become a new device (just as it happened when ditching the PATA driver for SATA, and /dev/hda became /dev/sda), your partitions/volumes won't mount. Instead, you should either be using LABELs or UUIDs. >> if I look in /dev/disk/by-id I can locate the following >> and in /dev/disk/by-uuid (again excuse the word wrap) >> >> lrwxrwxrwx 1 root root 10 Jun 21 19:20 >> f3408fda-0649-414f-8446-c01cf4e07558 -> ../../dm-0 >> >> There seems to be no correspondence between them If you're running LVM2, then you need to be familiar with the LVM commands. In particular, lvdisplay: # lvdisplay --- Logical volume --- LV Name /dev/work/root VG Name work LV UUID M5qcO0-CEBb-rn7M-tm2o-pgII-0HmE-LNuSW9 LV Write Access read/write LV Status available # open 1 LV Size 18.80 GiB Current LE 4813 Segments 2 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 254:0 -- . O . O . O . . O O . . . O . . . O . O O O . O . O O . . O O O O . O . . O O O O . O O O
From: Camaleón on 23 Jun 2010 17:40 On Wed, 23 Jun 2010 13:02:36 -0600, Aaron Toponce wrote: > On 06/23/2010 09:47 AM, Camaleón wrote: >> On Wed, 23 Jun 2010 09:40:22 +0100, Alan Chandler wrote: >>> I feel I should move my entire /etc/fstab over to using uuids >> >> Mmm... any strong reason for doing that? :-) > > Whether or not these are his reasons, I can tell you why that is a wise > move. UUIDs are unique to the device/filesystem. The major advantage of > using UUIDs is that you don't have to worry about reordering of disks by > the kernel when it sees it in a different order than previous. Yes, I know. But if the installer has setup (by its own) as default method for naming devices the old one and I am not experiencing any problem with that, for sure I won't change that. If it ain't broke, don't fix it. >> I'm with Lenny and the old naming method ("/dev/sdx") is the default >> for "/etc/fstab". > > This isn't recommended, because if the Linux kernel developers change > drivers, and the drives become a new device (just as it happened when > ditching the PATA driver for SATA, and /dev/hda became /dev/sda), your > partitions/volumes won't mount. Instead, you should either be using > LABELs or UUIDs. I know, I know... but Lenny developers decided to go this way for any reason and I will respect that. I'm aware that nowadays any modern distribution is using "uuid" or "id" at least in "/etc/fstab" but as I said, I still have not seen any good reason to change it. Greetings, -- Camaleón -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/pan.2010.06.23.21.30.39(a)gmail.com
From: Paul E Condon on 24 Jun 2010 15:50 On 20100623_054331, Ron Johnson wrote: > On 06/23/2010 05:20 AM, Javier Barroso wrote: > >On Wed, Jun 23, 2010 at 10:40 AM, Alan Chandler > ><alan(a)chandlerfamily.org.uk>wrote: > > > >>I feel I should move my entire /etc/fstab over to using uuids > >> > [snip] > >> > >>Which do I use, and what does the other one mean? > >> > > > >Get your uuid from dumpe2fs -h /dev/vg/lv | grep UUID > > > >But /dev/vg/lv is a persistent name, so no sense changing it to uuid, or > >maybe I'm missing something ? > > > > Or use labels. In squeeze, a recent revision in pata support seemed to introduce rewriting /etc/fstab to reference all file systems via UUID. Before that, I had constructed a system using labels which was totally clobbered by the pata upgrade (which also suppressed all mention of /dev/hd[ab][123] ) I don't use LVM. Perhaps using LVM protects you from 'upgrades' from ata to pata. Or from future upgrades in pata support. But I'm inclined to believe that we are in for a spate of instability as pata is worked out in all its unintended ramifications. FYI, the UUID is just a 128 bit number that is stored in a 16 byte space in the superblock of the ext[234] file system. Mostly it is set to a random value by mke2fs when the fs is originally created. But it can also be set to a user designated (non-random?) value by tune2fs -U <UUID> device. -- Paul E Condon pecondon(a)mesanetworks.net -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/20100624194611.GG3048(a)big.lan.gnu
From: Aaron Toponce on 25 Jun 2010 09:50 On 06/23/2010 03:30 PM, Camaleón wrote: > On Wed, 23 Jun 2010 13:02:36 -0600, Aaron Toponce wrote: >> Whether or not these are his reasons, I can tell you why that is a wise >> move. UUIDs are unique to the device/filesystem. The major advantage of >> using UUIDs is that you don't have to worry about reordering of disks by >> the kernel when it sees it in a different order than previous. > > Yes, I know. > > But if the installer has setup (by its own) as default method for naming > devices the old one and I am not experiencing any problem with that, for > sure I won't change that. If it ain't broke, don't fix it. Sure. But you can also avoid breakage through proper administration. >> This isn't recommended, because if the Linux kernel developers change >> drivers, and the drives become a new device (just as it happened when >> ditching the PATA driver for SATA, and /dev/hda became /dev/sda), your >> partitions/volumes won't mount. Instead, you should either be using >> LABELs or UUIDs. > > I know, I know... but Lenny developers decided to go this way for any > reason and I will respect that. I'm aware that nowadays any modern > distribution is using "uuid" or "id" at least in "/etc/fstab" but as I > said, I still have not seen any good reason to change it. So, you blindly accept what the developers think is good for your system? I understand they're developers for a reason, but even developers make mistakes. And having "/dev/sd??" in your /etc/fstab just might be one of them. FWIW, when the kernel switched disk drivers from PATA to SATA for identifying IDE drives, I had already moved my /etc/fstab to UUIDs, and I didn't have a problem with the upgrade. Friends of mine, however, got to rescue their system, because it wouldn't boot. To each their own. -- . O . O . O . . O O . . . O . . . O . O O O . O . O O . . O O O O . O . . O O O O . O O O
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