LiveSSD: A Low-Interference RAID Scheme for Hardware Virtualized SSDs
You Zhou, Fei Wu, Weizhou Huang, Changsheng M. Xie · IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems · 2020
Hardware virtualization has been increasingly used to provide performance isolation between multiple tenants sharing an SSD. It exploits the SSD's highly parallel architecture by allocating dedicated flash dies to each tenant. On the other hand, intra-SSD RAID, which stripes data and parity across flash dies, is essential to enhance storage reliability, such as protecting data against die failures and read errors. However, parity updates introduce I/O interference, degrading tenants' performance significantly, and violating performance isolation. To solve this problem, we propose a low-interference RAID scheme for hardware virtualized SSDs, called LiveSSD. Flash pages with the same offset across dies constitute a stripe in a RAID-4 manner. High-speed NVRAM is employed as parity storage. Thus, LiveSSD allows each tenant to read/write its flash die(s) independently and avoids parity updates being a performance bottleneck. Nonetheless, parity updates introduce I/O interference during garbage collection, i.e., extra reads of invalid flash pages. LiveSSD actively conducts parity updates in advance by utilizing both page access feature of flash memory and idle time in workloads. Extensive simulation results show that LiveSSD enables RAID protection in a hardware-virtualized SSD with minimum I/O interference caused by parity updates.