[ceph-users] Snapshot space

Josy josy at colossuscloudtech.com
Mon Oct 9 14:14:20 PDT 2017

Thank you for your response!

If the cloned VM had written around 10Gbs of data, wouldn't the clone 
also show that much space?

Below is a list of the original image, the clone and new snapshots along 
with their sizes.

The clone is still only a few hundred megabytes, while the snapshot 
shows "10GB" of disk space.

[cephuser at ceph-las-admin-a1 ceph-cluster]$  rbd du 
warning: fast-diff map is not enabled for 
e01f31e94a65cf7e786972b915e07364-1. operation may be slow.
NAME                 PROVISIONED   USED
e01f31e94a65cf7e786972b915e07364-1 at d-1       61440M       10840M
e01f31e94a65cf7e786972b915e07364-1                 61440M 616M
<TOTAL>                61440M       11456M

On 09-10-2017 17:22, Jason Dillaman wrote:
> No -- it means that your clone had written approximately 10GB of space
> within the image before you created the first snapshot. If the
> "fast-diff" feature is enabled, note that it only calculates usage in
> object size chunks (defaults to 4MB) -- which means that even writing
> 1 byte to a 4MB object would flag the object as dirty (it's an
> upper-bound estimate).
> On Sun, Oct 8, 2017 at 12:01 PM, Josy <josy at colossuscloudtech.com> wrote:
>> Hello,
>> I noticed that when we create a snapshot of a clone, the first snapshot
>> seems to be quite large.
>> For example:
>> Clone VM is taking up 136MBs according to rbd du
>> First snapshot: 10GBs
>> Second snapshot: 104MBs
>> Third snapshot: 57MBs
>> The clone is a Windows virtual machine, which does take around 10GB if it
>> wasn't a clone. Does this mean that the first snapshot of a clone needs to
>> have a full copy of the original cloned image?
>> Ceph version : Luminous 12.2.1
>> _______________________________________________
>> ceph-users mailing list
>> ceph-users at lists.ceph.com
>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com

More information about the ceph-users mailing list