3:21 p.m.
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(a)redhat.com Red Hat, Inc.