If there’s a filesystem on the volume, running fstrim or mounting with the 
discard option might significantly reduce usage and block count.  

> On Nov 25, 2023, at 1:02 PM, Tony Liu <[email protected]> wrote:
> 
> Thank you Eugen! "rbd du" is it.
> The used_size from "rbd du" is object count times object size.
> That's the actual storage taken by the image in backend.
> 
> For export, it actually flattens and also sparsifies the image.
> In case of many small data pieces, the export size is smaller than du size.
> 
> 
> Thanks!
> Tony
> ________________________________________
> From: Eugen Block <[email protected]>
> Sent: November 25, 2023 12:17 AM
> To: [email protected]
> Subject: [ceph-users] Re: easy way to find out the number of allocated 
> objects for a RBD image
> 
> Maybe I misunderstand, but isn’t ’rbd du‘ what you're looking for?
> 
> Zitat von Tony Liu <[email protected]>:
> 
>> Hi,
>> 
>> Other than get all objects of the pool and filter by image ID,
>> is there any easier way to get the number of allocated objects for
>> a RBD image?
>> 
>> What I really want to know is the actual usage of an image.
>> An allocated object could be used partially, but that's fine,
>> no need to be 100% accurate. To get the object count and
>> times object size, that should be sufficient.
>> 
>> "rbd export" exports actual used data, but to get the actual usage
>> by exporting the image seems too much. This brings up another
>> question, is there any way to know the export size before running it?
>> 
>> 
>> Thanks!
>> Tony
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> 
> 
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