OPTR: Order-Preserving Translation and Recovery Design for SSDs with a Standard Block Device Interface

Consumer-grade solid-state drives (SSDs) guarantee very few things upon a crash. Lacking a strong disk-level crash guarantee forces programmers to equip applications and filesystems with safety nets using redundant writes and flushes, which in turn degrade the overall system performance. Although some prior works propose transactional SSDs with revolutionized disk interfaces to offer strong crash guarantees, adopting transactional SSDs inevitably incurs dramatic software stack changes. Therefore, most consumer-grade SSDs still keep using the standard block device interface.

This paper addresses the above issues by breaking the impression that increasing SSDs' crash guarantees are typically available at the cost of altering the standard block device interface. We propose Order-Preserving Translation and Recovery (OPTR), a collection of novel flash translation layer (FTL) and crash recovery techniques that are realized internal to block-interface SSDs to endow the SSDs with strong request-level crash guarantees defined as follows: 1) A write request is not made durable unless all its prior write requests are durable. 2) Each write request is atomic. 3) All write requests prior to a flush are guaranteed durable. We have realized OPTR in real SSD hardware and optimized applications and filesystems (SQLite and Ext4) to demonstrate OPTR's benefits. Experimental results show 1.27× (only Ext4 is optimized), 2.85× (both Ext4 and SQLite are optimized), and 6.03× (an OPTR-enabled no-barrier mode) performance improvement.