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From cloudstack-fan <cloudstack-...@protonmail.com.INVALID>
Subject Re: Snapshots on KVM corrupting disk images
Date Sun, 27 Jan 2019 19:45:16 GMT
Hello Sean,

It seems that you've encountered the same issue that I've been facing during the last 5-6
years of using ACS with KVM hosts (see this thread, if you're interested in additional details:
https://mail-archives.apache.org/mod_mbox/cloudstack-users/201807.mbox/browser).

I'd like to state that creating snapshots of a running virtual machine is a bit risky. I've
implemented some workarounds in my environment, but I'm still not sure that they are 100%
effective.

I have a couple of questions, if you don't mind. What kind of storage do you use, if it's
not a secret? Does you storage use XFS as a filesystem? Did you see something like this in
your log-files?
[***.***] XFS: qemu-kvm(***) possible memory allocation deadlock size 65552 in kmem_realloc
(mode:0x250)
[***.***] XFS: qemu-kvm(***) possible memory allocation deadlock size 65552 in kmem_realloc
(mode:0x250)
[***.***] XFS: qemu-kvm(***) possible memory allocation deadlock size 65552 in kmem_realloc
(mode:0x250)
Did you see any unusual messages in your log-file when the disaster happened?

I hope, things will be well. Wish you good luck and all the best!


‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, 22 January 2019 18:30, Sean Lair <slair@ippathways.com> wrote:

> Hi all,
>
> We had some instances where VM disks are becoming corrupted when using KVM snapshots.
We are running CloudStack 4.9.3 with KVM on CentOS 7.
>
> The first time was when someone mass-enabled scheduled snapshots on a lot of large number
VMs and secondary storage filled up. We had to restore all those VM disks... But believed
it was just our fault with letting secondary storage fill up.
>
> Today we had an instance where a snapshot failed and now the disk image is corrupted
and the VM can't boot. here is the output of some commands:
>
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> [root@cloudkvm02 c3be0ae5-2248-3ed6-a0c7-acffe25cc8d3]# qemu-img check ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> qemu-img: Could not open './184aa458-9d4b-4c1b-a3c6-23d28ea28e80': Could not read snapshots:
File too large
>
> [root@cloudkvm02 c3be0ae5-2248-3ed6-a0c7-acffe25cc8d3]# qemu-img info ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> qemu-img: Could not open './184aa458-9d4b-4c1b-a3c6-23d28ea28e80': Could not read snapshots:
File too large
>
> [root@cloudkvm02 c3be0ae5-2248-3ed6-a0c7-acffe25cc8d3]# ls -lh ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> -rw-r--r--. 1 root root 73G Jan 22 11:04 ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
>
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> We tried restoring to before the snapshot failure, but still have strange errors:
>
> ------------------------------------------------------------------------------------
>
> [root@cloudkvm02 c3be0ae5-2248-3ed6-a0c7-acffe25cc8d3]# ls -lh ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> -rw-r--r--. 1 root root 73G Jan 22 11:04 ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
>
> [root@cloudkvm02 c3be0ae5-2248-3ed6-a0c7-acffe25cc8d3]# qemu-img info ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> image: ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> file format: qcow2
> virtual size: 50G (53687091200 bytes)
> disk size: 73G
> cluster_size: 65536
> Snapshot list:
> ID TAG VM SIZE DATE VM CLOCK
> 1 a8fdf99f-8219-4032-a9c8-87a6e09e7f95 3.7G 2018-12-23 11:01:43 3099:35:55.242
> 2 b4d74338-b0e3-4eeb-8bf8-41f6f75d9abd 3.8G 2019-01-06 11:03:16 3431:52:23.942
> Format specific information:
> compat: 1.1
> lazy refcounts: false
>
> [root@cloudkvm02 c3be0ae5-2248-3ed6-a0c7-acffe25cc8d3]# qemu-img check ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> tcmalloc: large alloc 1539750010880 bytes == (nil) @ 0x7fb9cbbf7bf3 0x7fb9cbc19488 0x7fb9cb71dc56
0x55d16ddf1c77 0x55d16ddf1edc 0x55d16ddf2541 0x55d16ddf465e 0x55d16ddf8ad1 0x55d16de336db
0x55d16de373e6 0x7fb9c63a3c05 0x55d16ddd9f7d
> No errors were found on the image.
>
> [root@cloudkvm02 c3be0ae5-2248-3ed6-a0c7-acffe25cc8d3]# qemu-img snapshot -l ./184aa458-9d4b-4c1b-a3c6-23d28ea28e80
> Snapshot list:
> ID TAG VM SIZE DATE VM CLOCK
> 1 a8fdf99f-8219-4032-a9c8-87a6e09e7f95 3.7G 2018-12-23 11:01:43 3099:35:55.242
> 2 b4d74338-b0e3-4eeb-8bf8-41f6f75d9abd 3.8G 2019-01-06 11:03:16 3431:52:23.942
>
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Everyone is now extremely hesitant to use snapshots in KVM.... We tried deleting the
snapshots in the restored disk image, but it errors out...
>
> Does anyone else have issues with KVM snapshots? We are considering just disabling this
functionality now...
>
> Thanks
> Sean



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