Arch Linux

switch86

Member

Registered: 2008-08-25

Posts: 24

LVM with external USB drive (no boot)

Sorry for a long post in advance. Takes breath.

I am stuck at the moment trying to recover an LVM.  I have two IDE disks in the LVM in addition to an external USB drive (three disks total).  I installed Arch to an LVM using just the internal drives and later added the external. The /boot partition is on a regular ext partition. Right now, the system will boot (the kernel image is accessible) but the logical volume (mounted to /) cannot be mounted, apparently because the system is attempting to mount the LVM before the USB device has been brought up. The PV that resides on the external drive is not found when the volume manager scans for PVs.

Or that's what it seems - my guess is the hook for lvm2 is being parsed before the USB hook (speculation on my part - right now I can't confirm the order of the hooks in /etc/mkinitcpio).

So, right now, I'm going to try to mount the LVM from a live CD (I'm using an image I downloaded and burned today) but can't get it mounted, because I seem to be short a device node for the LVM. Once I mount it, on my hunch, I plan to modify mkinitcpio to see if putting the USB hook first allows the volume manager to find the PV on the external drive.

Probably relevant info from various commands run while booted into the Live CD. When booted into the Live CD, I can see all the PVs as well as the VG and LV. The three PVs are part of a single VG, and the entire VG is my LV (mounted to /). /dev/sdc is the external drive.

pvscan
  PV /dev/sda3   VG volgroup   lvm2 [75.64 GB / 0    free]
  PV /dev/sdb2   VG volgroup   lvm2 [73.55 GB / 0    free]
  PV /dev/sdc1   VG volgroup   lvm2 [149.05 GB / 0    free]
  Total: 3 [298.25 GB] / in use: 3 [298.25 GB] / in no VG: 0 [0   ]

vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "volgroup" using metadata type lvm2

lvscan
  inactive          '/dev/volgroup/lvol' [298.25 GB] inherit

lvdisplay
  --- Logical volume ---
  LV Name                /dev/volgroup/lvol
  VG Name                volgroup
  LV UUID                5aJrSC-VP57-Fj9t-ZwVa-PBLG-HvzZ-4uB1Ti
  LV Write Access        read/write
  LV Status              NOT available
  LV Size                298.25 GB
  Current LE             76351
  Segments               3
  Allocation             inherit
  Read ahead sectors     auto

So, how to get the device node created? I've run vgscan --mknodes to no avail - lvdisplay claims the node is at /dev/volgroup/lvol, but the device node isn't there. Thus, when I attempt to mount using that device node, the output is that the special device node is not present. Anybody have a handy guide for mounting LVMs from a Live disk?

(I have more output, but I think this is a start.)

I suppose another option for now may be to remove the external from the volume group, but that would require shrinking the file system (not possible because, like an idiot, I used XFS).

Last edited by switch86 (2009-01-06 21:21:50)