Greetings ! I created a MD RAID6 with a 512KiB chunk size out of 12 8TB drives, no internal bitmap and no journal on quad xeon gold 6154 running kernel 4.18 (Ubuntu 18.04.1) and set FIO to do a 1TiB sequential write to the device with a block size of 5M, 3 processes and a QD of 64. Each drive being able to achieve 215MiB/s at the beginning of the drive, I expected the output to be somewhere around the 2GiB/s mark at the beginning of the raid array. After setting stripe_cache_size to 32768 and group_thread_cnt to 2, I only got an average 1.4GiB/s out of my array and the throughput wasn't very stable. I did the same test against a hardware raid controller, the Broadcom MegaRAID 9480-8i8e, and it managed a nice flat 1.9 GiB/s. I expected a modern cpu to easily win over a hardware controller but that wasn't the case. Am I missing something ? Many Thanks ! JDG
