Reiser5 Pursuing Selective File Migration For Moving Hot Files To High Performance Disks
Reiser5 has been working on new features like local volumes with parallel scaling out, data tiering and burst buffers, and other new features. The latest feature being worked on by Shishkin for Reiser5 is selective file migration.
One of the use-cases for Reiser5 selective file migration would be moving of hot files (frequently accessed) to higher performing drives on a system and pinning them for yielding better performance. Obviously there are other use-cases as well where you may want certain files stores stored on certain drives in a multi-device setup.
Shishkin sent out a mailing list post outlining the file-system's selective file migration work. Here's the summary:
Earlier any migration of data blocks in reiser5 logical volumes occurred only in the context of some volume balancing procedure, which actually is a massive migration, aiming to keep fairness of distribution on the whole logical volume. Typically such migrations complete some volume operations, e.g. adding a device to a logical volume, removing a device from a logical volume, increasing data capacity of a device, flushing a proxy-device, etc).
Now user can perform selective data migration. That is, migrate only data of some specified regular file to any specified device-component of the logical volume.
Also, for any specified regular file user can mark it as "immobile", so that volume balancing procedures will ignore that file.
Finally, for any specified regular file user can clear its "immobile" status, so that the file will be movable again by volume balancing procedures.
He has also published new Reiser5 patches both for the kernel module and user-space programs. Those latest Reiser5 patches can be found via SourceForge.