The Linux kernel has several software RAID algorithms, and selects the one that is fastest on your CPU. Isn't that always the same algorithm then ? No, definitely not. Newer CPUs have additional instructions that help speed things up. And it's not just clock speed that matters, memory bandwidth plays an important role too.
- On an old Pentium II Xeon 450 MHz, raid5 uses p5_mmx, and raid6 uses mmxx2. Software raid6 calculations are 72% slower than raid5.
- On a Pentium IV Xeon 1.5 GHz, raid5 using pIII_sse, and raid6 uses sse2x2. Software raid6 calculations are 12% slower than raid5.
- On an AMD Athlon XP2000+ (1.6 GHz), raid5 uses pIII_sse, raid6 uses sse1x2. Software raid6 calculations are 42% faster than raid5.
- On a AMD Athlon64 XP3400 (2.4 GHz), raid5 uses generic_sse, raid6 uses sse2x4 (raid6 44% slower than raid5).
- On a Xeon 5160 3GHz, raid5 uses generic_sse, raid6 uses sse2x4 (raid6 15% slower than raid5).
- Same algorithms on a Xeon X5450 3GHz (raid6 20% slower than raid5).
- Same algorithms on a Xeon E5430 2.66GH (raid6 18% slower than raid5).
- Same algorithms again on a Xeon X5650 2.66GHz (raid6 15% slower than raid5).
Posts
4 comments:
Very interesting!
Do you know what it's been used when running on an Intel® Atom™ Processor D510 1.66GHz (Dual-Core) 32Bit??
Cheers,
Didier
@deinoscloud: the QNAP Linux kernel doesn't report it in dmesg, apparently. I did try to find that info, of course :-) What did you expect ? ;-)
@deinoscloud: found it: on the Atom CPU in my QNAP raid 5 uses pIII_sse, measured at 5120 MB/s, and raid6 uses sse2x2, measured at 1082 MB/s.
These are the same algorithms as on the 32-bit Pentium IV CPU I tested. Performance for raid5 is 2.5x higher for comparable clock speed, but raid6 performance is only half.
The raid5 performance is far above
Of course, being a NAS device, the CPU in the QNAP is basically free to do this, so the CPU overhead is not slowing down other tasks, as long as it doesn't become a bottleneck. And with 4 cores available to spread other tasks over, I don't see it becoming a bottleneck soon.
Awesome. Thx for the info!
Post a Comment