Is there a way to figure out if
/dev/dm-1 is a block device partition or a whole block device? If
/dev/dm-1 is a partition, is there a way to find out the path to the corresponding whole block device?
Every partition is a "whole" block-device. You could sub-partition any partition, and then sub-partition it again, and again ...
In your example
dm-1 could be mapped to anything, a raw device, a dmcrypt device abstraction, a logical volume on a MD-RAID-backed, multi-pathed, dm-crypted volume group.
dm-X basically was just an arbitrary free number when the device was initialized. On hosts without many changes in the block device layer during runtime these numbers are just allocated in natural order at bootup.
But most device mapper mechanisms also allow you to specify an alias for your mapping. Check out
ls -l /dev/mapper/.
To then visualize the hierarchical relationships between block devices you can use the
lsblk (List block-devices). Shortened example output below:
$ lsblk /dev/sdb NAME MAJ:MIN TYPE sdb 8:128 disk ├─sdb1 8:129 part └─sdb5 8:133 part └─crypto (dm-0) 252:0 crypt ├─ubuntu-root (dm-1) 252:1 lvm └─ubuntu-swap (dm-2) 252:2 lvm
The lsblk command is a convenient way of displaying information about block devices including which device mapper device goes where.
For a given dm-x with major M, minor m, there is a corresponding
/sys/dev/block/M:m/dm/uuid file. If the content of the
uuid file starts with
part, it is safe to assume it is a partition. The corresponding whole device is found in
/sys/dev/block/M:n/slaves/. For instance:
[centos@try ~]$ cat /sys/dev/block/253:0/dm/uuid mpath-353333330000007d0 [centos@try ~]$ cat /sys/dev/block/253:1/dm/uuid part1-mpath-353333330000007d0 [centos@try ~]$ ls -l /sys/dev/block/253:1/slaves total 0 lrwxrwxrwx. 1 root root 0 15 août 22:06 dm-0 -> ../../dm-0
/dev/dm-1 is for "device mapper n.1".
Basically, it is a logical unit carved out using the kernel embedded device mapper layer. From a userspace application point of view, it is a RAW block device.
lvdisplay we should be able to tell you the specific physical disk/partition backing it.