On Sun, Jan 27, 2008 at 08:11:35PM +0000, Peter Grandi wrote: > >>> On Sun, 27 Jan 2008 20:33:45 +0100, Keld Jørn Simonsen > >>> <keld@xxxxxxxx> said: > > keld> Hi I have tried to make a striping raid out of my new 4 x > keld> 1 TB SATA-2 disks. I tried raid10,f2 in several ways: > > keld> 1: md0 = raid10,f2 of sda1+sdb1, md1= raid10,f2 of sdc1+sdd1, md2 = raid0 > keld> of md0+md1 > keld> 2: md0 = raid0 of sda1+sdb1, md1= raid0 of sdc1+sdd1, md2 = raid01,f2 > keld> of md0+md1 > keld> 3: md0 = raid10,f2 of sda1+sdb1, md1= raid10,f2 of sdc1+sdd1, chunksize of > keld> md0 =md1 =128 KB, md2 = raid0 of md0+md1 chunksize = 256 KB > keld> 4: md0 = raid0 of sda1+sdb1, md1= raid0 of sdc1+sdd1, chunksize > keld> of md0 = md1 = 128 KB, md2 = raid01,f2 of md0+md1 chunksize = 256 KB > > These stacked RAID levels don't make a lot of sense. > > keld> 5: md0= raid10,f4 of sda1+sdb1+sdc1+sdd1 > > This also does not make a lot of sense. Why have four mirrors > instead of two? My error, I did mean f2. Anyway 4 mirrors would make the disk 2 times faster than 2 disks, and given disk prices these days this could make a lot of sense. > Instead, try 'md0 = raid10,f2' for example. The first mirror of > will be striped across the outer half of all four drives, and > the second mirrors will be rotated in the inner half of each > drive. > > Which of course means that reads will be quite quick, but writes > and degraded operation will be slower. > > Consider this post for more details: > > http://www.spinics.net/lists/raid/msg18130.html Thanks for the reference. There is also more in the original article on possible layouts of what is now known as raid10,f2 http://marc.info/?l=linux-raid&m=107427614604701&w=2 including performance enhancements due to use of the faster outer sectors, and smaller average seek times because you can seek on only half the disk. 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
