Hi,
I'm trying to start Qemu on top of RBD. In documentation[1] there is a
big warning:
Important
If you set rbd_cache=true, you must set cache=writeback or risk data
loss. Without cache=writeback, QEMU will not send flush requests to
librbd. If QEMU exits uncleanly in this configuration, filesystems
on top of rbd can be corrupted.
But in last part of that page there is written that Qemu command line
override ceph.conf settings and setting *cache=writethrough* will force
*rbd_cache**=**true* and *rbd_cache_max_dirty=0*. In that configuration
rbd will write directly to Ceph and there is no risk of data loss
(except for things cached in VM OS). Am I right or am I missing something?
1: http://ceph.com/docs/master/rbd/qemu-rbd/
Thanks,
PS
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