On Monday June 14, thunder7@xxxxxxxxx wrote: > I am trying to convince my boss our new database-server wants raid-0+1, > not raid-5, and I got an idea while reading endless articles about > raid-5 being slow when writing and management not listening. You want numbers, not abstract arguments. Configure your server with raid5 and do some performance measurements - preferably with your database suite. Then reconfigure with raid 0+1 and test again. Show the numbers to your boss. You get to choose which numbers to show :-) > > suppose you make a 3-disc raid-5 without parity: > > data disc1 disc2 disc3 > A A A B > B B C C > > How would that perform compared to raid-5 and raid-0+1? Should be slightly better than raid1 of 2 drives, and slower than raid 0+1 on 4 drives. How it compares with raid-5 depends largely on load characteristics. With only 3 drives, some loads will very often provide raid5 with both data blocks in a stripe, and so no pre-reading will be needed. I hope to release a "raid10" module for 2.6 within a couple of weeks. raid10 is basically a combination of raid1 and raid0 all in one module with some interesting geometry possibilities. This particular geometry is one of the possibilities. > > There is a problem with extending this: you need groups of 3 disks. > Then again, compared to raid-0+1 you need fewer disks. There is no problem extending this. With 4 discs it would be A A B B C C D D which is a lot like raid0 over raid1 With 5 disks is would be A A B B C C D D E E or, if you wanted more redundancy: A A A B B B C C C D D D E E E The more discs you have, the faster it should be. > > Has this ever been implemented? Even better, benchmarked? Implemented: I'm fairly sure it has. Not in Linux just yet. Benchmarks: I don't know of any details. NeilBrown - 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
