On 08/17/2009 02:08 AM, Edward Siefker wrote: > I originally set up raid-luks-lvm on this machine with debian's > installer tool, now I am trying to add another encrypted raid1 device to > the existing volume group. I already have the raid device set up and > encrypted, that's no problem. Now the linux gazette > (http://linuxgazette.net/140/pfeiffer.html) tells me I should run > 'pvcreate' on the device in /dev/mapper. However, if I examine my > existing physical volumes with 'pvscan' I get the following: > > iblis:/home/hatta# pvscan > PV /dev/dm-0 VG iblis-volumes lvm2 [931.32 GB / 0 free] > Total: 1 [931.32 GB] / in use: 1 [931.32 GB] / in no VG: 0 [0 ] Which version of libdevmapper/dmsetup do you use? > Apparently I am using /dev/dm-0 instead of /dev/mapper/md1_crypt. I > wondered if these were maybe two names for the same thing, so I checked > ls: > > iblis:/home/hatta# ls -ld /dev/dm-0 /dev/mapper/md1_crypt > brw-rw---- 1 root disk 253, 0 2009-08-16 12:02 /dev/dm-0 > brw-rw---- 1 root disk 253, 0 2009-08-16 12:02 /dev/mapper/md1_crypt > > Same major and minor number, if that means anything. Well, from functional point of view they are same - they point to the same device, of course. But dmsetup/lvm itself does not create the /dev/dm-X nodes - the ones in /dev/mapper are the right and official ones that should always be used. The /dev/dm-X nodes are created by some general udev rules, dm-X is only internal kernel name for that device and you can't rely on those names (because the number X that is assigned is not stable and could be changed - it depends on the sequence of device activation). > iblis:/home/hatta# dmsetup info /dev/dm-0 > Device /dev/dm-0 not found > Command failed ..just forget that /dev/dm-X exists :) The thing is that these nodes shouldn't be there with recent versions of libdevmapper/dmsetup used in all distros.. HOWEVER, there has been some work done on udev support in LVM upstream lately (version 2.02.51, which also includes dmsetup/libdevmapper). Also, new udev rules have been added to support device mapper devices. When this udev support is enabled (it's still disabled by default though), the /dev/dm-X nodes are created directly by device-mapper rules, then /dev/mapper/ symlinks that point to /dev/dm-X (and /dev/<vgname>/<lvname> symlinks that point to /dev/dm-X as well for LVM devices). The reason for doing so is that creating nodes root /dev directory is considered to be the "standard way". Nevertheless, you should always use /dev/mapper! > iblis:/home/hatta# dmsetup info /dev/mapper/md1_crypt > Name: md1_crypt > State: ACTIVE > Read Ahead: 256 > Tables present: LIVE > Open count: 7 > Event number: 0 > Major, minor: 253, 0 > Number of targets: 1 > > > It works on one, and not the other. So they're not the same thing. My > new device 'md2_crypt' corresponds to /dev/dm-8, if I am to trust the > major/minor numbers. Should I run pvcreate on /dev/dm-8 or > /dev/mapper/md2_crypt? Alays use /dev/mapper. This is the only reliable way :) Peter _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
