[openstack-dev] [Ceph] Is it necessary to flatten Copy-on-write cloning for RBD-backed disks?

Kun Feng fengkun32 at gmail.com
Tue Jun 9 03:34:51 UTC 2015

Hi all,

I'm using ceph as storage backend for Nova and Glance, and merged the
rbd-ephemeral-clone patch into Nova. As VM disks are Copy-on-write clones
of a image, I have some concerns about this:

1. Since hundreds of vm disks based on one base file, is there any
performance problems that IOs are loaded on this one paticular base file?

2. Is it possible that the data of base file is damaged or PG/OSD
containing data of this base file out of service, resulting as all the VMs
based on that base file malfunctioned?

If so, flattening Copy-on-write clones may do some help. Is it necessary to
do it?
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