I'm reposting this as a Question. This same post was posted a few days ago as a discussion and no one from NetApp responded. On a side note how about adding a feature to the forum that lets us change a discussion to a question for when we forget to check teh "Mark this thread as a Question" checkbox.
In the NetApp University class on VMWare the subject of misalignment is discussed. The infomration covererd about performance makes perfect sense. However, new information I hadn't heard before was also shared. Partners are being told that misalignment also affects Data Deduplication. If you review the attached lab manual and go to page 5-7 (PDF Page 123) you will see the following section.
- Data deduplication impact of misalignment
- Not completely clear
- A customer experienced 6% savings then 64% space savings after properly aligning virutual disks
The the two statements above lead to a lot of questions. The first point says it isn't complely clear what the impact is and then it goes on to show a customer who had a huge space savings due to it. Well, if that really was related to misalignment then it is pretty clear. Unless the point is that NetApp isn't really sure the misalignment was the issue.
While the statement alone would leave the reader to believe "it isn't clear" the instructor teaching the class made it seem much more like a fact that proper alignment helps deduplication.
To be clear I'm all for proper alginment for performance reasons. However, I have 5 or 6 cusotomers who have not aligned any of their VMs and each is seeing a huge space savings with data deduplication.
Keep in mind that migrating from misalignment LUNs to aligned LUNS requires moving all the data. A number of things could have changed during that process to affect deduplication.
In the end I have the following questions:
- Has there been any testing internal to NetApp to substatiate what this customer belives they saw?
- How exactly does alignment affect data dedulplication alone?
- If all the VMs are misaligned by the same offset then wouldn't they fall on the same boundries in the 4KB blocks and thus still apear as duplicates?
