Improving software RAID with a write-ahead log

What this post added

This post introduces the implementation of a write-ahead log for software RAID 5/6 to address the 'write hole' problem, improve rebuild performance, and optimize write performance. The solution involves writing data and parity to a log on an SSD before persistent writes to RAID disks, ensuring consistency after power failures and enabling aggregation of writes to avoid read-modify-write penalties. The implementation details include metadata structures, checksum mechanisms, and reclaim strategies. Performance testing with different disk configurations is presented, along with future work on NVRAM/NVDIMM support and further write performance improvements.