hummmm nice i asked it because there´s many questions about is hardware raid better than software raid? i think that software is easier to implement and cpu (intel x86) is easier to upgrade than a arm(fpga or another) hardware raid cpu but thinking about raid software i never read anything about cpu use/memory use now i see it´s very small footprint for raid0/raid1, just checksum make thinks slower raid != 0/1 could we implement a "real" hardware raid? what´s "real"? a cpu just for raid, a memory just for raid (fixed size) maybe with linux cpu afinity, and linux max memory use? ok it´s not a good ide, but for benchmarks it´s the best scenario, and we will never get a "on high load your software raid can be slower..." got the problem? it´s not a numeric optimization, it´s just a human feeling (social? professional?) "optimization" and we know that we will always have a portion of memory and a portion of cpu just for raid =) 2011/1/19 NeilBrown <neilb@xxxxxxx>: > On Wed, 19 Jan 2011 22:14:45 -0200 Roberto Spadim <roberto@xxxxxxxxxxxxx> > wrote: > >> Hi, i wass thinking about cpu/memory use >> i have a dual (three four) cpu >> could i make linux to only use cpu1 for raid? and others to anythink >> else, don´t migrate raid between cpus... and don´t allow others >> programs to use raid cpu... >> is it possible? >> is it dificult? >> it´s more linux related feature, not raid related, but could we implement it? >> what about memory usage? how many memory software raid use? is it per >> device, per raid, does it have a hard limit (offcourse)? could we >> calculate it? for example i want raid1 with two disks of 1tb, how many >> memory should i buy? >> > > For levels other than RAID4/5/6, md/raid does not use any significant amount > of CPU or memory. > > For RAID4/5/6, md's use for CPU is single-threads so it will only use a > single CPU - which ever one the scheduler allocates it to from time to time. > > The only room for improvement that I can see would be to allow the 'xor' > calculation to be run in parallel on multiple CPUs and that would only help > if the storage devices were nearly as fast as a CPU. Where we have tried > parallelising xor, it has only made things slower. > > > For your particular question about RAID1 - use a RAID1 across two devices > would use less than 100K more than using just one of the devices. > During resync it might use as much as a couple of megabytes of extra memory. > > NeilBrown > -- > 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 > -- Roberto Spadim Spadim Technology / SPAEmpresarial -- 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
