[lvm-devel] lvthin: Why does vg/pool sit on top of vg/pool-tpool?

[Eric Wheeler]

Hello all,

Today I noticed that data/pool0 is a linear DM target backed by 
data-pool0-tpool:

brw-rw----. 1 root disk 253,    8 May 23 10:40 /dev/mapper/data-pool0
brw-rw----. 1 root disk 253,    6 May 30 15:45 /dev/mapper/data-pool0_tdata
brw-rw----. 1 root disk 253,    5 May 30 15:45 /dev/mapper/data-pool0_tmeta
brw-rw----. 1 root disk 253,    7 May 30 15:45 /dev/mapper/data-pool0-tpool

data-pool0-tpool: 0 188743680 thin-pool 253:5 253:6 128 0 0 
data-pool0_tdata: 0 188743680 linear 252:16 322560
data-pool0_tmeta: 0 2097152 linear 252:16 189066240
data-pool0: 0 188743680 linear 253:7 0


I noticed that /sys/block/dm-8/holders/ is empty, so nothing is using it. 

What is pool0 used for?

Does LVM somehow use the linear pool0 volume internally?

--
Eric Wheeler