>Hi, >I am using linux 2.6.8 for my research on raid systems. > >I need to have the disks of an array out of sync for a while. >I want to be able to stop a disk request queue (blk_stop_queue) and >start it sometime later. Meanwhile its mirrors should be serving r/w >as if this mirror was up. >Whenever the stopped mirror comes back it will serve all the requests >already sent to it. > >I am queueing up the requests sent to all others while my mirror queue >is stopped. > >The problem is that the other mirrors stop serving as well. Even if I >don't stop the queue, only delay its request a little bit, still the >others also slow down. > >Question: how do I get raid to allow mirrors to be out of sync? > >Obviously, I am missing something out in the code. > >Any clues? > >Thanks, >Ana Paula Ana: You are making this way too hard for yourself If you want to stop the queue but let the RAID system continue processing the queue, then just sending I/O from whatever program you are using to generate the load. This won't let you start up with a partially unflushed queue, but if for whatever reason you need to measure effects of pending I/Os and timing, then you can obtain a reasonably good simulation by increasing the queue depth and repeating the test. As for A way to get RAID (I assume software RAID, a la the md driver), to get out of sync is to "remove" a disk drive. If you are afraid to crack the case, then use a cheap USB enclosure for one of the disks and then turn it off or unplug the USB connector. You can also "remove" a disk by sending it a command to go into a self-test, perform a low-level format, send a mode select to change the block size, there are lots of ways if you think outside of the box. All of these "failure" scenarios will interact differently, just turning a disk drive off creates a real failure, not a quasi-emulated more graceful failure that may be easier for you to time and measure the effects. Good luck. David @ santools.com -- 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
