RAID 5 parity layout left-symmetric vs right symmetric vs other choices

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.

Kind regards,
Laszlo Budai

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/[email protected]/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/