On Wed, 2009-04-29 at 17:26 +0200, Thomas Glanzmann wrote: > 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? > 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. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
