On Mon, Jan 23, 2012 at 5:21 AM, Ted Ts'o <tytso@xxxxxxx> wrote: > On Sun, Jan 22, 2012 at 11:31:31AM +0800, Robin Dong wrote: >> > At the end of the day, thinp target is a very powerful tool, but >> > is does not fit all use cases. In particular, it fragments the >> > on-disk layout of ext4 metadata and benchmark results for how this >> > affect performance were never published. > > Amir, > > Well, to be fair, your approach to snapshotting also causes > fragmentation. If a file or a directory in the base image gets > modified while there is a read-only snapshot, the inode in the base > image gets fragmented as a result. Yes, that's true, to some extent. directory inodes, however, do not get fragmented. all journaled metadata is copied a side on JBD hooks. My claim was about fragmentation of ext4 metadata, but fragmentation of data is also a problem in both approaches. > > It is true that thin provisioning in general tends to defeat the block > placement algorithms used by a file system, but it will be possible to > create snapshots of non-thinp volumes, which will address this issue. > Hopefully in the next 3-6 months, these things will be implemented > enough so that we can benchmark them and see for certain how well or > poorly this approach will work out. I'm sure there will be a certain > number of tradeoffs for both approaches. > > Regards, > > - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
