Description of the Dmdedup target in Documentation. Signed-off-by: Vasily Tarasov <tarasov@xxxxxxxxxxx> --- Documentation/device-mapper/dm-dedup.txt | 51 ++++++++++++++++++++++++++++++ 1 files changed, 51 insertions(+), 0 deletions(-) create mode 100644 Documentation/device-mapper/dm-dedup.txt diff --git a/Documentation/device-mapper/dm-dedup.txt b/Documentation/device-mapper/dm-dedup.txt new file mode 100644 index 0000000..11bb7c2 --- /dev/null +++ b/Documentation/device-mapper/dm-dedup.txt @@ -0,0 +1,51 @@ +* 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., +virtual machine disk images collection and backups) deduplication provides a +significant amount of space savings. + +To quickly identify duplicates, Dmdedup maintains an index of hashes for all +written blocks. The block is a user-configurable unit of deduplication with +a default block size equal to 4KB. Dmdedup index, along with other +deduplication metadata, resides on a separate block device, which we refer +to as metadata device. Although the metadata device can be on any block +device, e.g., an HDD or its partition, for higher performance we recommend +to use SSD devices to store metadata. + +To create a new Dmdedup instance, a user can use the standard dmsetup tool: + +echo "0 $DMDEDUP_DEV_SIZE dedup data_dev=$DATA_DEV metadata_dev=$META_DEV \ + mdbackend=cowbtree reconstruct=no" | dmsetup create mydedup + +where + - $DMDEDUP_DEV_SIZE is the logical block device size in sectors; + - $DATA_DEV is the block device where the data will reside + (e.g., /dev/hdb); + - $META_DEV is the block device where the metadata + will reside (e.g., /dev/hdc). + +The mdbackend parameter specifies the metadata backend that should be used +for storing metadata. Supported backends are "cowbtree" and "inram." +Cowbtree uses the device-mapper's persistent API to store metadata. The +inram backend stores all meta-data in RAM as a hash table. + +The "reconstruct= parameter specifies if one wants to reconstruct a +previously created Dmdedup target (e.g., after a reboot). Specifying +"reconstruct=no" reinitializes a metadata device with an empty device. + +* AUTHORS + +Dmdedup was developed in the File system and Storage Lab (FSL) at Stony +Brook University Computer Science Department, in collaboration with Harvey +Mudd College and EMC. + +Key people involved in the project were Vasily Tarasov, Geoff Kuenning, +Sonam Mandal, Karthikeyani Palanisami, Philip Shilane, Sagar Trehan, and +Erez Zadok. + +We also acknowledge the help of several students involved in the +deduplication project: Teo Asinari, Deepak Jain, Mandar Joshi, Atul +Karmarkar, Meg O'Keefe, Gary Lent, Amar Mudrankit, Ujwala Tulshigiri, and +Nabil Zaman. -- 1.7.1 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
