> 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.

Writeback/writethrough also would affect writes only, so it should
have quite little bearing on backup jobs, which usually are 99.99%
read operations of various kinds.


-- 
May the most significant bit of your life be positive.
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