On Wed, Feb 2, 2011 at 16:27, Budai Laszlo <laszlo.budai@xxxxxxxxx> wrote: > Hello everybody, > > can someone direct me to some documentation describing the pros and cons > for choosing a certain layout. > Any explanation on this topic is welcome. > There's very little difference between the different raid5 layouts; the default left-symmetric should be good for almost everything. Right/left refers to how the parity blocks are distributed between disks, and should have no real impact on performance. Symmetric/asymmetric refers to how the data blocks adjacent to the parity blocks are ordered, with symmetric having a slight performance advantage for large sequential I/O. The other raid5 layouts are special cases for reshaping & should be automatically handled by mdadm; or are DDF-compatible layouts, intended to give "a basic level of interoperability between different suppliers of RAID technology" [5]. Links for more detailed info: 1 - http://www.issociate.de/board/goto/25704/raid5_parity_algorithm.html - the next two links I got from here. 2 - http://www.accs.com/p_and_p/RAID/LinuxRAID.html 3 - http://www.pdl.cmu.edu/PDL-FTP/Declustering/ASPLOS.ps - Post Script file. 4 - http://www.mail-archive.com/misc@xxxxxxxxxxx/msg90952.html - from OpenBSD's mailing list, questioning their use of left-asymmetric as the default, when symmetric is expected to have a slight advantage for large sequential I/O, and the thread starter hadn't been able to find any advantages for asymmetric. Linux MD raid defaults to left-symmetric. 5 - http://www.snia.org/tech_activities/standards/curr_standards/ddf/ -- 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
