nice, but raid1 is not a very cpu consuming (a filesystem can use more cpu than a raid implementation...) a browser (firefox) too i think raid1 source code is well otimized for cpu and memory, maybe you need a faster cpu and not a less cpu consuming software, maybe a hardware raid could help you... 2011/1/31 Keld Jørn Simonsen <keld@xxxxxxxxxx>: > On Tue, Feb 01, 2011 at 07:42:57AM +1100, NeilBrown wrote: >> On Mon, 31 Jan 2011 14:11:31 +0100 Keld Jørn Simonsen <keld@xxxxxxxxxx> wrote: >> >> > On Mon, Jan 31, 2011 at 09:37:46AM +0000, Mathias Burén wrote: >> > > On 31 January 2011 08:52, Keld Jørn Simonsen <keld@xxxxxxxxxx> wrote: >> > > > If your intallation is CPU bound, and you are >> > > > using an Atom N270 processor or the like, well some ideas: >> > > > >> > > > The Atom CPU may have threading, so you could run 2 RAIDs >> > > > which then probably would run in each thread. >> > > > It would cost you 1 more disk if you run 2 RAID5's >> > > > so you get 8 TB payload out of your 12 GB total (6 drives of 2 TB each). >> > > > >> > > > Another way to get better performance could be to use less >> > > > CPU-intensitive RAID types. RAID5 is intensitive as it needs to >> > > > calculate XOR information all the time. Maybe a mirrored >> > > > raid type like RAID10,f2 would give you less CPU usage, >> > > > and the run 2 RAIDS to have it running in both hyperthreads. >> > > > Here you would then only get 6 TB payload of your 12 GB disks, >> > > > but then also probably a faster system. >> > > > >> > > > Best regards >> > > > keld >> > > > >> > > >> > > Hi, >> > > >> > > It's interesting what you say about the XOR calculations. I thought >> > > that it was only calculated on writes? The Atom (330) has HT, so Linux >> > > sees 4 logical CPUs. >> > >> > Yes you are right, it only calculates XOR on writes with RAID5. >> > But then I am puzzled what all these CPU cycles are used for. >> > Also many cycles are used on mirrored raid types. Why? >> > Maybe some is because of LVM? I have been puzzled for a long time why >> > ordinary RAID without LVM need to use so much CPU. Maybe a lot of data >> > sguffling between buffers? Neil? >> >> What is your evidence that RAID1 uses lots of CPU? > > Much of this is raid10, but it should be the same: > http://home.comcast.net/~jpiszcz/20080329-raid/ > http://home.comcast.net/~jpiszcz/raid/20080528/raid-levels.html > > It seems like cpu usage is rather proportionate to the IO done. > And the CPU usage does get up to about 40 % for reading, and > 45 % for writing - this is most likely a significant delay factor. > For slower CPUs like the Atom CPU this may be an even more significant > delay factor. > > For RAID5 the situation is even worse, as expected. > > best regards > keld > -- > 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
