I guess i was not clear enough. i am using raid5 over 3 maxtor disks. the chunk size is 1MB. i mesured the io coming from one disk alone when I READ from it with 1MB buffers , and i know that it is ~32MB/s. I created raid0 over two disks and my throughput grown to 64 MB/s. Doing the same thing with raid5 ended in 32 MB/s. I am using async io since i do not want to wait for several disks when i send an IO. By sending a buffer which is striped aligned i am supposed to have one to one relation between a disk and an io. iostat show that all of the three disks work but not fully. On 1/3/06, Mark Hahn <hahn@xxxxxxxxxxxxxxxxxxx> wrote: > > I am checking raid5 performance. > > reads or writes? > > > I am using asynchronous ios with buffer size as the stripe size. > > why do you think async matters? > > > In this case i am using a stripe size of 1M with 2+1 disks. > > do you mean that md says you have 512k chunks? > > > Unlike raid0 , raid5 drops the performance by 50% . > > that's slightly unclear: -50% relative to what? a raw single disk? > is this reads or writes? strictly bandwidth, and if so, do you have > multiple outstanding reads? > > > Is it because it does parity checkings ? > > non-degraded R5 doesn't do parity checks on reads, afaik. > > -- Raz - 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
