On Tue, Feb 1, 2011 at 4:01 AM, David Brown <david@xxxxxxxxxxxxxxx> wrote: > On 31/01/2011 23:52, Keld JÃrn Simonsen wrote: >> >> raid1+0 and Linux MD raid10 are similar, but significantly different >> in a number of ways. Linux MD raid10 can run on only 2 drives. >> Linux raid10,f2 has almost RAID0 striping performance in sequential read. >> You can have an odd number of drives in raid10. >> And you can have as many copies as you like in raid10, >> > > You can make raid10,f2 functionality from raid1+0 by using partitions. For > example, to get a raid10,f2 equivalent on two drives, partition them into > equal halves. ÂThen make md0 a raid1 mirror of sda1 and sdb2, and md1 a > raid1 mirror of sdb1 and sda2. ÂFinally, make md2 a raid0 stripe set of md0 > and md1. > > If you have three disks, you can do that too: > > md0 = raid1(sda1, sdb2) > md1 = raid1(sdb1, sdc2) > md2 = raid1(sdc1, sda2) > md3 = raid0(md0, md1, md2) > > As far as I can figure out, the performance should be pretty much the same > (although wrapping everything in a single raid10,f2 is more convenient). The performance will not be the same because. Whenever possible, md reads from the outermost portion of the disk -- theoretically the fastest portion of the disk (by 2 or 3 times as much as the inner tracks) -- and in this way raid10,f2 can actually be faster than raid0. -- Jon -- 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
