Some information is missing to give a helpful answer. How do you backup? (Files? RBD via Ceph? Block Device with qemu-img? Which Device driver do you use (Virtio? SATA?). In our production we use Virtio RBD and the Hypervisor standard cache mode. The Disks are snapshoted before the backup with 'qemu-img', e. g.: virsh snapshot-create-as VM backup-VM --diskspec vda,file=/snapshots/backup-snapshot-VM-vda.raw --disk-only --atomic --quiesce --no-metadata qemu-img convert -O raw rbd:libvirt-pool/VM.raw /backup/VM.raw -p virsh blockcommit VM vda --wait --active --pivot The backup process is as fast as expected. Am Mi., 30. Nov. 2022 um 16:09 Uhr schrieb Dominique Ramaekers < dominique.ramaekers@xxxxxxxxxx>: > > Hi, > > I was wondering... > > In Ceph/Libvirt docs only cachmodes writetrough and writeback are discussed. My clients's disks are all set to writeback in the libvirt client xml-definition. > > For a backup operation, I notice a severe lag on one of my VM's. Such a backup operation that takes 1 to 2 hours (on a same machine but) on local LVM storage, takes on a ceph storage 6 hours. Though I have to say that the cachemode on the local LVM storage is set on directsync. > > => So what if I played around with other cachemodes? Will it make a difference? > > I'm trying now cachemode 'unsafe' so tonight I should measure the difference if there is any. > > Input will be greatly appreciated. > > Greetings, > > Dominique. > > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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