Device Mapper Notations and LVM

Linux and Unix-Like Red Hat
1

Hi,

I had a doubt regarding device mapper notations and their corresponding LVM volumes.

I have configured a volume group with two logical volumes in it as root and swap.

The entries in the /etc/fstab file show the dm notations namely,

/dev/mapper/VolGroup00-LogVol01
/dev/mapper/VolGroup00-LogVol02

instead of,

/dev/VolGroup00/LogVol01
/dev/VolGroup00/LogVol02

Also swapon -s command gives the dm notation, i.e /dev/mapper/VolGroup00-LogVol02 instead of the actual LVM path.

Is this normal behaviour or have I done something wrong?

Also, is there a way to find a mapping between the device mapper
notations and the corresponding lvm volumes?

Thanks,
KK

2

When using SCSI devices, the path is clearly defined based on the SCSI ID of the controller, the port that the device is connected to, etc.

SATA/SAS drives do not have this luxury, as they are not defined on a chain. This causes some confusion, as when /dev/sda comes up next time, it may be /dev/sdc.

dev-mapper uses a different, non-volatile ID such as UUID or disk label (contained in metadata) to keep disk paths consistent, through its abstraction.

Basically, the short version is:

To make sure that your devices are named and in a consistent path, dev-mapper handles the devices so that your / is found properly each bootup and is not confused with /tmp or some other file system on another device.

3

Yes, it is normal.

Yes. Remove "/mapper", replace '-" with "/". Thus

/dev/mapper/VolGroup00-LogVol01

becomes

/dev/VolGroup00/LogVol01