On Tue, Dec 22, 2009 at 07:08:25PM +0200, Ciprian Dorin, Craciun wrote: > 2009/12/22 Keld Jørn Simonsen <keld@xxxxxxxxxx>: > > On Tue, Dec 22, 2009 at 06:34:55PM +0200, Ciprian Dorin, Craciun wrote: > >> Hello all! > >> > >> I've created a 64G RAID 1 matrix from 3 real disks. (I intend to > >> use this as a target for backups.) > >> Now while playing around with this array, I've observed that the > >> read performance is quite low because it always reads from the disk in > >> the first slot (which happens to be the slowest...) > >> > >> So my questions are: > >> * is there any way to tell the MD driver to load-balance the reads > >> between the three disks? > > > > It does not make sense to do distributed reading in raid1 for sequential > > files. This is because it will not be faster to read from more drives, > > as this will only make the reading from one drive skipping blocks on > > that drive. In other words, in the time you use for skipping blocks on > > one drive, you could just as well have read the blocks. So then better > > just read all the blocks off one drive, and then do other possible IO > > from other drives. > > Aha. It makes sens now. But, does it mean that if I have parallel > IO's (from different read operations) they are going to be distributed > between the disks? It should, but I am not fully sure it does. But try it out with two concurrent reads of two big files, and then watch it with iostat 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
