Hello all! We are experiencing a strange problem with QEMU virtual machines where the virtual machine image is hosted on a gluster volume. Access via fuse. (Our GFAPI attempt failed, it doesn’t seem to work properly with current QEMU/distro/gluster).
We have the volume tuned for ‘virt’.
So we use qemu-img to create a raw image. You can use sparse or falloc with equal results. We start a virtual machine (libvirt, qemu-kvm) and libvirt/qemu points to the fuse mount with the QEMU image file we created.
When we create partitions and filesystems – like you might do for installing an operating system – all is well at first. This includes a root XFS filesystem.
When we try to re-make the XFS filesystem over the old one, it will not mount and will report XFS corruption.
If you dig into XFS repair, you can find a UUID mismatch between the superblock and the log. The log always retains the UUID of the original filesystem (the one we tried to replace). Running xfs_repair doesn’t truly repair, it just reports
more corruption. xfs_db forcing to remake the log doesn’t help.
We can duplicate this with even a QEMU raw image of 50 megabytes. As far as we can tell, XFS is the only filesystem showing this behavior or at least the only one reporting a problem.
If we take QEMU out of the picture and create partitions directly on the QEMU raw image file, then use kpartx to create devices to the partitions, and run a similar test – the gluster-hosted image behaves as you would expect and there is
no problem reported by XFS. We can’t duplicate the problem outside of QEMU.
We have observed the issue with Rocky 9.4 and SLES15 SP5 environments (including the matching QEMU versions). We have not tested more distros yet.
We observed the problem originally with Gluster 9.3. We reproduced it with Gluster 9.6 and 10.5.
If we switch from QEMU RAW to QCOW2, the problem disappears.
The problem is not reproduced when we take gluster out of the equation (meaning, pointing QEMU at a local disk image instead of gluster-hosted one – that works fine).
The problem can be reproduced this way:
- Assume /adminvm/images on a gluster sharded volume
- rm /adminvm/images/adminvm.img
- qemu-img create -f raw /adminvm/images/adminvm.img 50M
Now start the virtual machine that refers to the above adminvm.img file
- Boot up a rescue environment or a live mode or similar
- sgdisk --zap-all /dev/sda
- sgdisk --set-alignment=4096 --clear /dev/sda
- sgdisk --set-alignment=4096 --new=1:0:0 /dev/sda
- mkfs.xfs -L fs1 /dev/sda1
- mkdir -p /a
- mount /dev/sda1 /a
- umount /a
- # MAKE same FS again:
- mkfs.xfs -f -L fs1 /dev/sda1
- mount /dev/sda1 /a
- This will fail with kernel back traces and corruption reported
- xfs_repair will report the log vs superblock UUID mismatch I mentioned
Here are the volume settings:
# gluster volume info adminvm
Volume Name: adminvm
Type: Replicate
Volume ID: de655913-aad9-4e17-bac4-ff0ad9c28223
Status: Started
Snapshot Count: 0
Number of Bricks: 1 x 3 = 3
Transport-type: tcp
Bricks:
Brick1: 172.23.254.181:/data/brick_adminvm_slot2
Brick2: 172.23.254.182:/data/brick_adminvm_slot2
Brick3: 172.23.254.183:/data/brick_adminvm_slot2
Options Reconfigured:
storage.owner-gid: 107
storage.owner-uid: 107
performance.io-thread-count: 32
network.frame-timeout: 10800
cluster.lookup-optimize: off
server.keepalive-count: 5
server.keepalive-interval: 2
server.keepalive-time: 10
server.tcp-user-timeout: 20
network.ping-timeout: 20
server.event-threads: 4
client.event-threads: 4
cluster.choose-local: off
user.cifs: off
features.shard: on
cluster.shd-wait-qlength: 10000
cluster.shd-max-threads: 8
cluster.locking-scheme: granular
cluster.data-self-heal-algorithm: full
cluster.server-quorum-type: server
cluster.quorum-type: auto
cluster.eager-lock: enable
performance.strict-o-direct: on
network.remote-dio: disable
performance.low-prio-threads: 32
performance.io-cache: off
performance.read-ahead: off
performance.quick-read: off
cluster.granular-entry-heal: enable
storage.fips-mode-rchecksum: on
transport.address-family: inet
nfs.disable: on
performance.client-io-threads: on
Any help or ideas would be appreciated. Let us know if we have a setting incorrect or have made an error.
Thank you all!
Erik
