Research On Transaction Support For Deduplication-based Solid State Drives

Integrating deduplication inside solid state drive(SSD)can effectively decrease the data written to SSD as well as erase operations,hence the flash wearing is lessened.The out-ofplace update of flash memory gives it the inherent advantage of supporting transaction.It can effectively reduce the overhead of managing transactions for file systems using transaction design in SSDs.A deduplication-based SSD with a transactional interface can combine the advantages of both features to provide high-performance transaction support.The deduplication in SSDs introduces additional metadata and makes it more complex for transaction management.As a result,the consistency between these data and metadata must be guaranteed when implementing transaction processing in deduplication-based SSDs since the inconsistency between data and metadata will lead to a transaction failure.To solve the above problems,a Transactional FTL for Deduplication-based SSDs(TxDedup)is proposed,which efficiently supports transaction and ensures consistency of the data and metadata in deduplication-based SSDs.Tx-Dedup modifies and extends the existing interface of SSDs to provide transactional interface for upper software.Tx-Dedup adopts a Transaction Table(Tx-Table)to record the status of transactions and the metadata of every write operation within each transaction;delays the update of metadata information such as address mapping and fingerprint,and prohibits the write operation of uncommitted transaction from modifying the hash table index and the address mapping table to support transactional atomicity;redesigns the read and write procedure of deduplicated data to ensure the isolation between different transactions.Furthermore,we modify the file system(ext4)and block device driver to verify the functionality of Tx-Dedup,enabling them to take advantage of the transaction support of Tx-Dedup and reduce the overhead of transaction management of file system.We implement and evaluate our Tx-Dedup design on an OpenSSD hardware platform.The results of experiment prove that(1)Tx-Dedup can increase IOPS by 5%~24.1% and 38.5%~68.5% respectively,compared with a general deduplication-based SSD with the ordered mode file system and the full journaling mode file system;(2)Tx-Dedup can reduce read and write response time by up to 22% and 37%,compared with a general deduplicationbased SSD with the ordered mode file system;and achieves less read and write response time compared with a general deduplication-based SSD with the full journaling mode file system.