Question to Deduplication Ratio

[Skywalker]

Hi guys
hopefully my last questions to you guys. However, I still have a question regarding the dedup ratio.
This is for me with a dataset at 1.99

is there a reason why it is not exactly 2.00? Is there a setting that can be made in this regard (though I haven't seen anything here).

thanks again!

 

[Arwen]

Why would you expect it to be exactly 2.00?

Based on the size, I am guessing you setup a test environment. Note that some overhead blocks, (aka metadata like directory entry blocks), may not be de-duplicatable. Thus, if you had a file that you then copied over into a different path, (so same file data blocks), it would be de-duplicated. But, not it's directory entry.

Last, in general, people with questions about de-dup for ZFS should not be using de-dup for ZFS. It boils down to specialized knowledge, specific hardware requirements and an understanding when to beef up hardware.

Of course, if you are just experimenting for learning, go for it.

 

[Skywalker]

Why would you expect it to be exactly 2.00?

Based on the size, I am guessing you setup a test environment. Note that some overhead blocks, (aka metadata like directory entry blocks), may not be de-duplicatable. Thus, if you had a file that you then copied over into a different path, (so same file data blocks), it would be de-duplicated. But, not it's directory entry.

Last, in general, people with questions about de-dup for ZFS should not be using de-dup for ZFS. It boils down to specialized knowledge, specific hardware requirements and an understanding when to beef up hardware.

Of course, if you are just experimenting for learning, go for it.

thank you very much for your answer. Indeed, I test certain settings and behaviors regarding the data reduction within the TrueNAS, so I am not enough in all details (yet)
I had in fact seen a video before where a rate of 2.00 was achieved although a similar approach was taken.
But I understand your arguments, makes sense. Thanks a lot!

 

[Arwen]

Your welcome.

I wrote a forum Resource on ZFS De-Duplication:

Resource - ZFS de-Duplication - Or why you shouldn't use de-dup

The TrueNAS forums occasionally have people who come across ZFS de-duplicate, and want to investigate its use. Or think it is a good idea, and want to implement it. Here are some suggested configuration details: Understand that you need CPU...

www.truenas.com

It's not perfect, various forum members will chime in and we will improve it.

The intent of the Resource is not to stop users from using ZFS De-Duplication, but to have informed users of that feature. Some will be dissuaded from using de-dup, and they will have a better experience with TrueNAS because of it. Others will be able to have clues and reasons why things are the way they are, so less surprised with their use of de-dup.