This is a request for comments for Dmdedup. Dmdedup is a device-mapper deduplication target. Every write coming to the Dmdedup instance is deduplicated against previously written data. For datasets that contain many duplicates scattered across the disk (e.g., collections of virtual machine disk images and backups) deduplication provides a significant amount of space savings. To quickly identify duplicates, Dmdedup maintains an index of hashes for all written blocks. A block is a user-configurable unit of deduplication with a default block size of 4KB. Dmdedup's index, along with other deduplication metadata, resides on a separate block device, which we refer to as a metadata device. Although the metadata device can be on any block device, e.g., an HDD or its own partition, for higher performance we recommend to use SSD devices to store metadata. Dmdedup is designed to support pluggable metadata backends. A metadata backend is responsible for storing metadata: LBN-to-PBN and HASH-to-PBN mappings, allocation maps, and reference counters. (LBN: Logical Block Number, PBN: Physical Block Number). Currently we implemented "cowbtree" and "inram" backends. The cowbtree uses device-mapper persistent API to store metadata. The inram backend stores all metadata in RAM as a hash table. Our preliminary experiments on real traces (FIU traces from http://iotta.snia.org/tracetypes/3) demonstrate that Dmdedup can even exceed the performance of a disk drive running ext4. The reasons are that (1) deduplication reduces I/O traffic to the data device, and (2) Dmdedup effectively sequentializes random writes to the data device. Dmdedup is developed by a joint group of researchers from Stony Brook University, Harvey Mudd College, and EMC. See the documentation patch for more details. Vasily Tarasov (10): dm-dedup: main data structures dm-dedup: core deduplication logic dm-dedup: hash computation dm-dedup: implementation of the read-on-write procedure dm-dedup: COW B-tree backend dm-dedup: inram backend dm-dedup: Makefile changes dm-dedup: Kconfig changes dm-dedup: status function dm-dedup: documentation Documentation/device-mapper/dm-dedup.txt | 51 ++ drivers/md/Kconfig | 8 + drivers/md/Makefile | 2 + drivers/md/dm-dedup-backend.h | 114 +++++ drivers/md/dm-dedup-cbt.c | 724 ++++++++++++++++++++++++++++ drivers/md/dm-dedup-cbt.h | 44 ++ drivers/md/dm-dedup-hash.c | 148 ++++++ drivers/md/dm-dedup-hash.h | 30 ++ drivers/md/dm-dedup-kvstore.h | 51 ++ drivers/md/dm-dedup-ram.c | 585 +++++++++++++++++++++++ drivers/md/dm-dedup-ram.h | 43 ++ drivers/md/dm-dedup-rw.c | 248 ++++++++++ drivers/md/dm-dedup-rw.h | 19 + drivers/md/dm-dedup-target.c | 760 ++++++++++++++++++++++++++++++ drivers/md/dm-dedup-target.h | 100 ++++ 15 files changed, 2927 insertions(+), 0 deletions(-) create mode 100644 Documentation/device-mapper/dm-dedup.txt create mode 100644 drivers/md/dm-dedup-backend.h create mode 100644 drivers/md/dm-dedup-cbt.c create mode 100644 drivers/md/dm-dedup-cbt.h create mode 100644 drivers/md/dm-dedup-hash.c create mode 100644 drivers/md/dm-dedup-hash.h create mode 100644 drivers/md/dm-dedup-kvstore.h create mode 100644 drivers/md/dm-dedup-ram.c create mode 100644 drivers/md/dm-dedup-ram.h create mode 100644 drivers/md/dm-dedup-rw.c create mode 100644 drivers/md/dm-dedup-rw.h create mode 100644 drivers/md/dm-dedup-target.c create mode 100644 drivers/md/dm-dedup-target.h -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
