I&#x27;m sorry I am not sure I get it.
Let&#x27;s say you have a 1000 kB file which is duplicated and which is located on continuous blocks (so if the CDs used 2 kB boundaries, we&#x27;ll have 500 continuous blocks).
If ZFS use 128 kB block size, it will detect 7 blocks (896 kB) that it can deduplicate. So we only lose about 10%.<p>Perhaps there is a high degree of fragmentation then and files are not on continous blocks ?<p>(this example would be the same if instead of 2 exactly duplicated files, we have a big common chunk between 2 files)