Hello, as usual, I'm few years behind trends so I have learned about LVM thin volumes recently and I especially like that your volumes can be "sparse" - that you can have 1TB thin volume on 250GB VG/thin pool. Is it somehow possible to use that with libvirt? I have found this post from 2014: https://www.redhat.com/archives/libvirt-users/2014-August/msg00010.html which says you should be able to create "sparse" volume with `virsh vol-create ...` or that libvirt should be able to see thin volumes you create yourself, but neither of that works for me (libvirt-3.2.1-6.fc26.x86_64). This way I try to create new: # vgs storage VG #PV #LV #SN Attr VSize VFree storage 1 1 0 wz--n- 267.93g 0 # lvs storage -a LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert [lvol0_pmspare] storage ewi------- 68.00m lvol1 storage twi-aotz-- 267.80g 0.00 0.44 [lvol1_tdata] storage Twi-ao---- 267.80g [lvol1_tmeta] storage ewi-ao---- 68.00m # virsh pool-dumpxml storage <pool type='logical'> <name>storage</name> <uuid>f523aed2-a7e4-4dc2-88db-0193a7337704</uuid> <capacity unit='bytes'>287687311360</capacity> <allocation unit='bytes'>287687311360</allocation> <available unit='bytes'>0</available> <source> <device path='/dev/nvme0n1p3'/> <name>storage</name> <format type='lvm2'/> </source> <target> <path>/dev/storage</path> </target> </pool> # cat /tmp/big.xml <volume> <name>big</name> <capacity>1073741824</capacity> <allocation>1048576</allocation> <target> <path>/dev/storage/big</path> </target> </volume> # virsh vol-create storage /tmp/big.xml error: Failed to create vol from /tmp/big.xml error: internal error: Child process (/usr/sbin/lvcreate --name big -L 1024K --type snapshot --virtualsize 1048576K storage) unexpected exit status 5: Volume group "storage" has insufficient free space (0 extents): 1 required. When I create thin volume manually, I do not see it: # lvcreate -n big -V 500G --thinpool storage/lvol1 Using default stripesize 64.00 KiB. WARNING: Sum of all thin volume sizes (500.00 GiB) exceeds the size of thin pool storage/lvol1 and the size of whole volume group (267.93 GiB)! For thin pool auto extension activation/thin_pool_autoextend_threshold should be below 100. Logical volume "big" created. # lvs storage -a LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert big storage Vwi-a-tz-- 500.00g lvol1 0.00 [lvol0_pmspare] storage ewi------- 68.00m lvol1 storage twi-aotz-- 267.80g 0.00 0.45 [lvol1_tdata] storage Twi-ao---- 267.80g [lvol1_tmeta] storage ewi-ao---- 68.00m # virsh vol-list storage Name Path ------------------------------------------------------------------------------ Do I understand the concept incorrectly, or is there something else to configure? At the end I want to get max IO performance with possibility to "overcommit disk space". I know I can use storage "dir", but thought there might be something faster? Thank you very much for a response, Jan -- Jan Hutar Systems Management QA jhutar@redhat.com Red Hat, Inc.