Re: Data Deduplication with the help of an online filesystem check

Thomas Glanzmann
2009-06-04T08:49:19Z

Hello Chris,

> > My question is now, how often can a block in btrfs be refferenced?

> The exact answer depends on if we are referencing it from a single
> file or from multiple files. But either way it is roughly 2^32.

could you please explain to me what underlying datastructure is used to
monitor if the block is still referenced or already free? Is a counter
used, bitmap (but that can't be if is 2^32) or some sort of list? I
assume that a counter is used. If this is the case, I assume when a
snapshot for example is deleted the reference counter of every block
that was referenced in the snapshot will be decremented by one. Is this
correct or am I missing something here?

Thomas