Hi, i'm a university student in end phase and considering to write my master thesis about the md raid performance issues and to implement a prototype to solve it. What i have done and know: 1. I wrote a (internal) paper to measure raid performance with SSDs with freebsd software raid implementations and md raid under linux. I tested RAID 0 and RAID 5 with up to 6 Intel SSDs (X25-M G2, each 20k Write and 40k read OPS) and esp for RAID 5 it doesn't scaled. With my fio and general environment (bs 4k, iodepth 256, direct=1, randomwrite, spare capacity 87,5%, noop scheduler, latest mainline kernel from git, amd phenom II 1055T 2,8 GHz, 8GB ram) i got SSDs IOPS 3 14497.7 4 14005 5 17172.3 6 19779 2. AFAIK the main problem is that md uses only one write thread for each raid instance and their is a patch in work but still not availible. So my questions: 1. Is this problem solved (i know it isn't in mainline)? Is there still some work to do? 2. If not solved: Why isn't solved already (time? technical problem? priority? Not solvable?) 3. Is it the only problem? With my tests i captured detailed cpu stats and no cpu core was nearly at its capacity. So there are known other big reasons for perfomance issues? For example: 6 SSD randomwrite: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %idle all 1,17 0,00 12,67 12,71 3,27 3,05 0,00 0,00 67,13 0 1,41 0,00 7,88 15,42 0,07 0,15 0,00 0,00 75,07 1 0,00 0,00 38,04 3,14 19,20 18,08 0,00 0,00 21,54 2 1,50 0,00 7,55 14,78 0,07 0,02 0,00 0,00 76,08 3 1,09 0,00 7,31 12,15 0,05 0,02 0,00 0,00 79,38 4 1,35 0,00 7,41 12,94 0,07 0,00 0,00 0,00 78,23 5 1,65 0,00 7,78 17,84 0,12 0,03 0,00 0,00 72,57 4. Is this (bringing the raid performance to or near the theoretically performance) a work that a man can archieve in less then 6 months without practical experience in kernel hacking (and i'm not a genuis :( ) Thanks in advance for your responses, Peter Landmann -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
