3 Silver

Re: Can you measure dedupe by LUN or folder?

XtremIO does deduplication and compression at the global array level and not at the volume level. We therefore report the dedupe/compression ratio at the cluster level only.

Think a little about this.  If you have two volumes A and B, and write 4 blocks into the volumes.  Block 1 is unique and goes into volume A.  Block 2 is unique and goes into Volume B.  Blocks 3 and 4 are duplicates and are written into both Volume A and Volume B.

So now:

Volume A has 3 logical blocks and 1 physical

Volume B has 3 logical blocks and 1 physical

Two blocks are shared between volume A and B.

How would you account for the physical space of blocks 3 and 4?  You can’t assign it to either volume, or divide it between them.  Both methods are inaccurate.  What if you deleted blocks 3 and 4?  Where would you then assign the capacity?  It could suddenly cause a volume’s consumption to jump.

This is like a “divide by zero” math problem.  The answer is undefined.