I'd a appreciate any help/pointers in implementing the proposal below including the right path to get this into the kernel itself. ---------------------------------- I'm outlining below a proposal for a RAID device mapper virtual block device for the kernel which adds "split raid" functionality on an incremental batch basis for a home media server/archived content which is rarely accessed. Given a set of N+X block devices (of the same size but smallest common size wins) the SplitRAID device mapper device generates virtual devices which are passthrough for N devices and write a Batched/Delayed checksum into the X devices so as to allow offline recovery of block on the N devices in case of a single disk failure. Advantages over conventional RAID: - Disks can be spun down reducing wear and tear over MD RAID Levels (such as 1, 10, 5,6) in the case of rarely accessed archival content - Prevent catastrophic data loss for multiple device failure since each block device is independent and hence unlike MD RAID will only lose data incrementally. - Performance degradation for writes can be achieved by keeping the checksum update asynchronous and delaying the fsync to the checksum block device. In the event of improper shutdown the checksum may not have all the updated data but will be mostly up to date which is often acceptable for home media server requirements. A flag can be set in case the checksum block device was shutdown properly indicating that a full checksum rebuild is not required. Existing solutions considered: - SnapRAID (http://snapraid.sourceforge.net/) which is a snapshot based scheme (Its advantages are that its in user space and has cross platform support but has the huge disadvantage of every checksum being done from scratch slowing the system, causing immense wear and tear on every snapshot and also losing any information updates upto the snapshot point etc) I'd like to get opinions on the pros and cons of this proposal from more experienced people on the list to redirect suitably on the following questions: - Maybe this can already be done using the block devices available in the kernel? - If not, Device mapper the right API to use? (I think so) - What would be the best block devices code to look at to implement? Regards, Anshuman Aggarwal _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
