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? I would expect it to use very little, but I've been wrong before. 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
