On Friday March 16, mschwarz@xxxxxxxxxxxxx wrote: > I'm not a Linux newbie (I've even written a couple of books and done some > very light device driver work), but I'm completely new to the software > raid subsystem. > > I'm doing something rather oddball. I'm making an array of USB flash > drives and comparing read and write rates. > > Well, I've had great success writing. I've got seven flash drives on a > hub. I've joined them up both linear and raid0 and written large amounts > of data to them. But come time to read from them, linear works, but raid0 > hangs after transferring just shy of 2G of data. It doesn't matter if it > reading from one file or from many files whose cumulative size is just shy > of 2G. It doesn't matter if I'm using "dd" or "cp" to read the file or > files. > > The process doing the transfer is unkillable. Not with a kill -15 or a > kill -9. It won't die, but it also won't make progress. > > "Linear" always works. Raid-0 always hangs. My guess would be a locking bug in the usb storage driver or some lower level USB driver.. A significant difference between raid0 and linear is that a largish IO will touch all drives for raid-0, but only one or two for linear. That gives much more opportunity for locking bugs to hit. When it is in the hanging state, do echo t > /proc/sysrq-trigger and look in the kernel logs for the stack trace of all processes. Hopefully the stack trace for the processes in 'D' state will be informative. NeilBrown > > Here are my mdadm commands to create the array: > > mdadm --create /dev/md0 --level=linear --auto=md --chunk=32 > --raid-devices=7 /dev/sd? > > (The wildcard works because the seven flash drives are the only scsi > devices on the system). > > The command for the raid-0 array is the same as above except for the > "--level=0" it takes to make a raid 0 array. > > I then use "mkfs" to make the filesystem and mount the resulting array at > "/mnt" > > Can anyone give a raid newbiw some tips? Is there something obvious I'm > missing? Would it help to provide strace/ltrace/ptrace of the hanging copy > command? > > Any help (including URLs of manuals I should RTFM) would be most welcome. > > Thanks! > > > -- > Michael Schwarz > > > - > 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 - 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
