Re: Can you measure dedupe by LUN or folder?
If dedupe and compression is being done globally across all the data on the array (as it happens in XtremIO), you cannot determine a correct (or useful) dedupe/compression ratio at the LUN level.
For example, if the same data exists in two different volumes on the array, which volume do you give the dedupe benefit to? The volume where the data was written later? As you can see, it becomes arbitrary at that point.
What happens if that data is deleted from one of the volumes – do you suddenly remove the dedupe ratio for the second volume? You will start seeing data efficiency metric changes in one volume because of a change in some other volume.
Any vendor that shows volume level dedupe/compression ratios (when they claim to be implementing these data efficiency features at the array level) is at best a “guess".