You Can’t DeDupe Oracle DB FilesPosted: August 14, 2009
One of our storage vendors has DeDupe technology. DeDupe is short for deduplication – the idea is that when you have identical blocks on the storage, it will only keep one copy of the block. This is a nice idea that saves on storage. Its especially good on shared filesystems where many users keep copies of identical files.
Our vendor loves DeDupe and managed to convince my storage manager that DeDupe will lead to amazing storage savings. Even on the DB volumes! No matter how much the DBAs protested that DBs rarely have full blocks that are identical to each other, the vendor kept insisting that many other customers have seen amazing storage savings using this technology on their data files. “Databases have many empty blocks”, the storage manager said after lunch with the vendor “And they are all identical! Think how much space you can save by keeping just one empty block!”.
We agreed to test DeDupe. As expected, we saw about 2% of space savings. Not exactly what the storage manager expected.
I wasn’t surprised. Even empty data blocks in Oracle DB files are not really identical. They have a header, which contains a relative address, which makes each empty block slightly different.
So, no DeDupe. Thought you may want to know, so you won’t have to repeat this experience. Maybe even send a link to your vendor 🙂
If your experience was different though, I’d love to know. The vendor insisted that he had many custormers happily deduping their databases.