"Andrew Herdman" <andrew@whine.com> wrote: > Pardon me if my assumption was incorrect, but I was under the belief that > when using software RAID1, that when reads occurred on the RAID device that > it would read from both drives in a striped fashion similar to how RAID0 > works to improve the speed of the md devices. I am actually seeing this, > but it appears that the reads on each drive are continuing for 10 to 20 > seconds before moving onto the next drive and then another 10-20 seconds and > back again. This is not allowing for any performance increase, it just lets > the drives rest alternately. > > This link http://www.whine.com/~andrew/alternating_disk.png is a gkrellm > snapshot of the activity, hda and hde are the two disks in the RAID array. > Each disk is the master on it's own channel. Was that a single large file that you read or multiple files? As far as I could observe, the RAID1 code reads one file from one disk and never changes disks during this read - so you get the performance of one disk. *But* the code distributes different writes to different disks. Try the following: dd if=/dev/mdX of=/dev/null& Now watch gkrellm and see that it reads only from one disk. Then start another instance of dd. You will see that this instance reads from the other RAID disk. This way one disk can seek for a file while the other one is transfering one. A single read won't be faster but concurrent access to the same filesystem will be much faster than on a non-RAID filesystem. Cheers, Juri -- Juri Haberland <juri@koschikode.com> - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
