[Qemu-devel] QCOW2 deduplication key value store

["Benoît Canet" <benoit.canet@irqsave.net>]

Hello,

I am starting this thread so we can discuss of the choice of a good key/value
store for the QCOW2 deduplication.

One of the main goal is to keep the ratio between the number of cluster written
and the number of dedup metadata io high.

I initially though about taking the first two stages of SILT
(http://goo.gl/x7UcI) to build the key value store.

The very nice thing about the two first stage of SILT is that the write io
involved are not random at all: The log is obviously not random and the
conversion into the second stage hash table can be done sequentially.
This makes the io ratio very high.

Kevin later thought about combining the first stage of SILT with a big hash
table as a second stage.
While this method is simpler I don't understand how we can inject the first
stage into this big table without generating a log of random ios.

Best regards

Benoît