How to keep VM running when a storage domain is offline
Hello, I am trying to understand how I can prevent a VM from being paused when one of it's disks is unavailable due to a problem with the storage domain. The scenario: A VM with 3 disks. OS disk on a highly available domain. And Two large disks each on separate domains. (so a total of 3 domains). The two large disks are mirrored using ZFS - but when one of the storage domains goes down the VM pauses. Is is possible to configure the VM to not pause when certain storage domains are unavailable? So instead of getting Paused due to IO error the disk would just be missing until that domain was brought back online? Thanks, -Matthew
You need replicated gluster storage for that. So that one part of the storage can go down but two others still keep on running. And you need to set the threshold so that a quorum of 2 is sufficient (if you have replica 3). If the storage volume is offline. It would be the same as the same thing as if you pulled the hard drive from a server. So if ovirt wouldn't pause the virtual server then Linux would complain and set it to read only. On July 24, 2018 13:05:13 Matthew B <matthew.has.questions@gmail.com> wrote:
Hello,
I am trying to understand how I can prevent a VM from being paused when one of it's disks is unavailable due to a problem with the storage domain.
The scenario:
A VM with 3 disks. OS disk on a highly available domain. And Two large disks each on separate domains. (so a total of 3 domains).
The two large disks are mirrored using ZFS - but when one of the storage domains goes down the VM pauses. Is is possible to configure the VM to not pause when certain storage domains are unavailable? So instead of getting Paused due to IO error the disk would just be missing until that domain was brought back online?
Thanks, -Matthew _______________________________________________ Users mailing list -- users@ovirt.org To unsubscribe send an email to users-leave@ovirt.org Privacy Statement: https://www.ovirt.org/site/privacy-policy/ oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ List Archives: https://lists.ovirt.org/archives/list/users@ovirt.org/message/ICR64SPQO2EVXP...
On Tue, Jul 24, 2018 at 2:03 PM Matthew B <matthew.has.questions@gmail.com> wrote:
Hello,
I am trying to understand how I can prevent a VM from being paused when one of it's disks is unavailable due to a problem with the storage domain.
The scenario:
A VM with 3 disks. OS disk on a highly available domain. And Two large disks each on separate domains. (so a total of 3 domains).
This makes the vm depend on 3 storage domain - very fragile configuration. The two large disks are mirrored using ZFS - but when one of the storage
domains goes down the VM pauses. Is is possible to configure the VM to not pause when certain storage domains are unavailable? So instead of getting Paused due to IO error the disk would just be missing until that domain was brought back online?
I don't think we support this concept. When you start the vm, the disk must exists. If the disks are not needed when the vm starts, maybe you want to plug them to the vm later by your application, only if the disks are available? Even if you solved plugging the disks only when the storage is available, you need to handle errors while the disk is plugged to the vm. If qemu fail to read or write to the disk, it must choose: - pause the vm, so the I/O can be retried later when the vm is resumed - stop the vm, maybe the operation will succeed on another host - propagate the error the guest. This will like to make the file system in the guest read-only, which usually requires a restart of the vm to recover. The last option may work if the guest is using multipath, and multipath is configured to queue I/O forever on failures. Vdsm supports different error policy per drive, but I don't see any UI for setting this. You can see the error_policy in the vm xml, available in vdsm log when starting a vm, or using virsh virsh -r list find your vm id or name, and then: virsh -r dumpxml my-vm-name-or-id Arik, do we have a way to control error policy per disk? Another option is to mount the "optional" disks from within the vm, so your application inside the vm have full control when there is trouble to mount or access the optional disks. Nir
participants (3)
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Johan Bernhardsson -
Matthew B -
Nir Soffer