hi, i'm succesfully using gnbd as a single service for a long time. Now i discovered a weired problem with the gnbd devices with kernel 2.6.18. I build the gnbd.ko module out of the cvs tree. All works fine if you don't do to much an the gnbds. But if you stress test the devices, the gnbds will hang, e.g. reads and writes hang. If you restart the gnbd server, the client will continue to read and write until the next hang. So i first checked my gnbd servers and tried from 1.01 till 1.03 and the latest cvs. But the problem is still there. From another gnbd client i had no problem, with none of these gnbd server versions (i was impressed you can mix these versions). Also changing the kernel on the gnbd server didn't helped. So i was stick to the gnbd client with kernel 2.6.18. I have to use this kernel because of the new hardware. So i tried a little and found out that changing the default io scheduler for the gnbd devices on the client makes the hanging write and reads resume. The default scheduler was cfq and with this i can easily reproduce this behavior. With the deadline scheduler it doesn't. So i read a little about io scheduling on linux. And my assumption is a gnbd device shouldn't need any io scheduling, because the network has no latency when seeking like a hard disk. On the gnbd server there are getting request from more than one gnbd client, so scheduled io on the client would mix up the scheduling on the server. And also the server does its own io scheduling when writing to the real disk. So i could use the noop scheduler or have i missed something? Has anyone on the list more info about io scheduling and gnbd? -- greetings eMHa
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