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2013-08-29

LVM dm device mapping

When trying to find out where swap is in relation to LVM it is useful to know how "dm" devices map to LV's

swapon -s
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       11304952        0       -1

We can see that it's mapped to dm-1 which I'm unsure which logical volume that is. Running the following script will shed some light:
lvdisplay|awk  '/LV Name/{n=$3} /Block device/{d=$3; sub(".*:","dm-",d); print d,n;}'
dm-0 Vol1
dm-1 Vol2
dm-2 Vol3

Alternatively, just look at the second column of Block device in lvdisplay

dm-1
Block device 253:1

Or an even better way is using dmsetup
dmsetup ls
Log-LogVol00    (253:2)
OS-LogVol01     (253:3)
OS-LogVol00     (253:0)
Data-LogVol00   (253:1)

The number after the colon is the dm-#

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