September 14, 2010Linux Software xen
Sometimes you will get in the need to directly mount an xvda device which is often used, if you (for example) install a debian virtual system in xen. Then this block device consists out of several partitions, which can not directly be used. But of course you can access the data of it, without the need of booting the guest os (domU).
This is the same if you get an iso or any other type block devices which uses multiple partion slices.
First we have to find out, at which position the slice (which we want to mount) start. For this we use the fdisk command which will give us all information we need. You do all this directly on the dom0, you dont have to boot the domU in any way!
xen ~ # fdisk -ul /dev/vg/server02 Disk /dev/vg/server02: 3221 MB, 3221225472 bytes 255 heads, 63 sectors/track, 391 cylinders, total 6291456 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00090c14 Device Boot Start End Blocks Id System /dev/vg/server02 * 2048 5894143 2946048 83 Linux Partition 1 does not end on cylinder boundary. /dev/vg/server02 5896190 6289407 196609 5 Extended Partition 2 does not end on cylinder boundary. /dev/vg/server02 5896192 6289407 196608 82 Linux swap / Solaris
The important things are:
Sector size -> 512
Start of the partition slice -> 2048
Now fire up an calculator and multiply these number to get the correct offset:
512 * 2048 = 1048576
With this value you can already mount the partition.
mount -o offset=1048576 /dev/vg/server02 /mnt/
That was easy or what do you think?