HI Ian just some points that you should consider... it's an idea about the theory... don't think it's a main guide to linux-raid or anything else... some basic things... a disk have one head arm, in other words it can read/write a sequence of bits, move, read/write more bits, move... etc when you use strip (raid-0, 5, 6, raid 10) you change how data is write, instead of a continous byte stream, you divide it in chunks... chunk 1 at disk 1 position 0, chunk 2 at disk 2 position 0, chunk 3 at disk1 position 1 .... etc... this place each disk close to one specific chunk example... considering a read from position 0 to last position of array: the disk used = chunk id % number_of_disks, with a chunk of 128MB and two disks, and reading 1GB you will read 0-128MB from disk 1, 128-256MB from disk 2, 256-384MB from disk 1 ... etc when you read more than one chunk, you use two heads arms (two disks) here you have speed boost, you must check what is the best chunk size for your work load, (and chunk should only be used when need, on some workloads raid1 is better) using two head you can read/write faster, but this is only nice for continous stream... when you need parallel works (many thread) you can use raid1 for read in parallel since it don't have chunks it can read data with only one disk, in other words... the workload can (when possible) be shared for 1 disk / thread, if you have 10 disks using raid-1, you can have a nice performace for 10 threads without problems, for write the slowest disk will stall the write performace, but you should consider what you need... that's a superficial explain, the implementation can be a bit different, but explain the idea about the use of chunks the workload tell what's better in my system sometimes raid1 is better than raid10 because i have many threads reading diferent parts of disk, in this case i can add many heads arms (disks) one for each important thread, and i have a good performace (considering a high load system), but if you need fast continous read, the chunk is VERY good for example if you need a read of 1GB, and have 10 disks, you can have a performace of 10x with a good chunk size, since each disk will be used when a chunk read is requested, and each disk can read parallel and continous (without many head movement) if you put a chunk size of 1GB and you need a read of 1GB, you don't have any performace boost from chunks... the best thing to do is TEST with your workload i think this can help, if not delete from your mail box :) -- 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
