[ovirt-devel] Re: Improving VM behavior in case of IO errors

On Tue, Aug 11, 2020 at 7:21 PM Kevin Wolf <kwolf(a)redhat.com&gt; wrote: > Am 11.08.2020 um 17:44 hat Nir Soffer geschrieben: > > On Mon, Aug 10, 2020 at 11:53 AM Kevin Wolf <kwolf(a)redhat.com&gt; wrote: > > > > > Am 09.08.2020 um 23:50 hat Nir Soffer geschrieben: > > > > On Wed, Jul 29, 2020 at 2:30 PM Shubha Kulkarni > > > > <shubha.kulkarni(a)oracle.com&gt; wrote: > > > > > > > > > > Thanks for the feedback Nir. > > > > > > > > > > I agree in general that having an additional engine config for disk > > > > > level error handling default would be the right way. It would be > good > > > to > > > > > decide the granularity. Would it make sense to have this for a > specific > > > > > disk type like lun or would you prefer to make it generic for all > > > types? > > > > > > > > This must be for a specific disk type, since for thin images on block > > > > storage we cannot support propagating errors to the guest. This will > > > > break thin provisioning. > > > > > > Is werror=enospc not enough for thin provisioning to work? This will > > > still stop the guest for any other kinds of I/O errors. > > > > > > > Right, this should work, and what we actually use now for propagating > > errors for anything but cdrom. > > Hm, wait, the options you quote below are all either 'stop' or 'report', > but never 'enospc'. Is 'enospc' used for yet another kind of disk? > Currently as a user there is no good way to get enospc, this is what Shubha is trying to fix. > For LUN using werror=enospc,rerror=enospc seems wrong, but we do this for > > many years. > > > > This is how we handle cdrom: > > > > -device > > > ide-cd,bus=ide.2,id=ua-346e176c-f983-4510-af4b-786b368efdd6,bootindex=2,werror=report,rerror=report > > Makes sense to me. This is read-only and removable media. Stopping the > guest usually makes sense so that it won't assume the disk is broken, > but if it happens with removable media, you can just eject and re-insert > the same image and it's fixed. > BTW this was changed since users typically leave cdrom attached with otherwise unused ISO storage domain (NFS). When the NFS server breaks the VM was stopped. > Image: > > > > -device > > > virtio-blk-pci,iothread=iothread1,scsi=off,bus=pci.5,addr=0x0,drive=libvirt-2-format,id=ua-1d93fa9e-1665-40d7-9ffc-770513242795,bootindex=1,write-cache=on,serial=1d93fa9e-1665-40d7-9ffc-770513242795,werror=stop,rerror=stop > > I assume this is the one that could use 'enospc'? > Yes, if we propagate errors, this will become werror=enospc,rerror=enospc > > > > LUN: > > > > -device > > > virtio-blk-pci,iothread=iothread2,scsi=off,bus=pci.7,addr=0x0,drive=libvirt-1-format,id=ua-19b06845-2c54-422d-921b-6ec0ee2e935b,write-cache=on,werror=stop,rerror=stop > > \ > > > > Kevin, any reason not to use werror=report,rerror=report for LUN when > > we want to propagate errors to the guest? > > If you want to propagate errors, then 'report' is the right setting. > > What does "LUN" mean exactly? When we attach a multipath device, this is called "Direct LUN" in oVirt. The underlying device can iSCSI or FC, managed by the user, or managed by Cindelib. We have 3 options: 1. As virtio or virtio-scsi <disk type='block' device='disk' snapshot='no'> <driver name='qemu' type='raw' cache='none' error_policy='stop' io='native' iothread='1'/> <source dev='/dev/mapper/360014058657c2a1941841348f19c1a50' index='1'> <seclabel model='dac' relabel='no'/> </source> <backingStore/> <target dev='vdb' bus='virtio'/> <alias name='ua-c1bf9168-00f0-422f-a190-9ddf6bcd449b'/> <address type='pci' domain='0x0000' bus='0x06' slot='0x00' function='0x0'/> </disk> -blockdev '{"driver":"host_device","filename":"/dev/mapper/360014058657c2a1941841348f19c1a50","aio":"native","node-name":"libvirt-1-storage","cache":{"direct":true,"no-flush":false},"auto-read-only":true,"discard":"unmap"}' \ -blockdev '{"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"raw","file":"libvirt-1-storage"}' \ -device virtio-blk-pci,iothread=iothread1,scsi=off,bus=pci.6,addr=0x0,drive=libvirt-1-format,id=ua-c1bf9168-00f0-422f-a190-9ddf6bcd449b,write-cache=on,werror=stop,rerror=stop \ 2. same + passthrough <disk type='block' device='lun' sgio='filtered' snapshot='no'> <driver name='qemu' type='raw' cache='none' error_policy='stop' io='native'/> <source dev='/dev/mapper/360014058657c2a1941841348f19c1a50' index='1'> <seclabel model='dac' relabel='no'/> </source> <backingStore/> <target dev='sda' bus='scsi'/> <alias name='ua-c1bf9168-00f0-422f-a190-9ddf6bcd449b'/> <address type='drive' controller='0' bus='0' target='0' unit='0'/> </disk> -blockdev '{"driver":"host_device","filename":"/dev/mapper/360014058657c2a1941841348f19c1a50","aio":"native","node-name":"libvirt-1-storage","cache":{"direct":true,"no-flush":false},"auto-read-only":true,"discard":"unmap"}' \ -blockdev '{"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"raw","file":"libvirt-1-storage"}' \ -device scsi-block,bus=ua-50240806-3d5a-4e5b-a220-bc394698a641.0,channel=0,scsi-id=0,lun=0,drive=libvirt-1-format,id=ua-c1bf9168-00f0-422f-a190-9ddf6bcd449b,werror=stop,rerror=stop \ 3. same + privileged I/O <disk type='block' device='lun' sgio='unfiltered' snapshot='no'> <driver name='qemu' type='raw' cache='none' error_policy='stop' io='native'/> <source dev='/dev/mapper/360014058657c2a1941841348f19c1a50' index='1'> <seclabel model='dac' relabel='no'/> </source> <backingStore/> <target dev='sda' bus='scsi'/> <alias name='ua-c1bf9168-00f0-422f-a190-9ddf6bcd449b'/> <address type='drive' controller='0' bus='0' target='0' unit='0'/> </disk> -blockdev '{"driver":"host_device","filename":"/dev/mapper/360014058657c2a1941841348f19c1a50","aio":"native","node-name":"libvirt-1-storage","cache":{"direct":true,"no-flush":false},"auto-read-only":true,"discard":"unmap"}' \ -blockdev '{"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"raw","file":"libvirt-1-storage"}' \ -device scsi-block,bus=ua-9c2c7e43-d32d-4ea4-9cfd-e2bb36d26fdb.0,channel=0,scsi-id=0,lun=0,drive=libvirt-1-format,id=ua-c1bf9168-00f0-422f-a190-9ddf6bcd449b,werror=stop,rerror=stop \ It doesn't seem to be passthrough, so is > it just that you have some restriction like that it's always raw? Yes, we don't support qcow2 for these disks (yet). Theoretically we can support qcow2 to enable incremental backup. But the qcow2 image will never be larger than the block device, actually smaller to leave room for metadata. Thin provisioning is done on the storage side. > Maybe > I would use 'enospc' for consistency even though you never expect this > error to happen. But 'report' is fine, too. > enospc looks wrong since this error should not be possible, and if it happens we cannot handle it. Sounds like good way to confuse futures maintainers of this code.

Maybe libvirt or qemu did not support "report" when this code was added in 2010?