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

Thomas Glanzmann
2009-04-29T15:26:14Z

Hello Chris,

> Your database should know, and the ioctl could check to see if the
> source and destination already point to the same thing before doing
> anything expensive.

I see.

> > So, if I only have file, offset, len and not the block number, is there
> > a way from userland to tell if two blocks are already point to the same
> > block?

> You can use the fiemap ioctl.

I see.

One more question, in my dedup test VMs, I had a block that was often
referenced these are the top block. The last one alone saves 3 Gbyte of
data. My question is now, how often can a block in btrfs be refferenced?

top 4 block counts for 8 Kbyte:

32055
59514
63606
415252

Thomas