On Sat, Jan 15, 2011 at 2:50 PM, Bart Kus <me@xxxxxxxx> wrote: > Some research has revealed a frightening solution: > > http://forums.gentoo.org/viewtopic-t-716757-start-0.html > > That thread calls upon mdadm --create with the --assume-clean flag. It also > seems to re-enforce my suspicions that MD has lost my device order numbers > when it marked the drives as spare (thanks, MD! Remind me to get you a nice > christmas present next year.). I know the order of 5 out of 10 devices, so > that leaves 120 permutations to try. I've whipped up some software to > generate all the permuted mdadm --create commands. > > The question now: how do I test if I've got the right combination? Can I dd > a meg off the assembled array and check for errors somewhere? I guess running a read-only fsck is the best way to proove it working. > > The other question: Is testing incorrect combinations destructive to any > data on the drives? Like, would RAID6 kick in and start "fixing" parity > errors, even if I'm just reading? > If you don't want to risk your data, you could create a cowloop of each device before writing to it, or dm snapshot using dmsetup. I made a script for dmsetup snapshot on the side when I really needed it because cowloop wouldn't compile. Here it is, it should help you understand how it works! RODATA=$1 shift COWFILE=$1 shift FSIZE=$1 shift PREFIX=$1 shift if [ -z $RODATA ] || [ -z $COWFILE ] || [ -z $FSIZE ] || [ ! -z $5 ] then echo "Usage: $0 [read only device] [loop file] [size of loop in MB] {prefix}" echo "Read only device won't ever get a write." echo "Loop file can be a file or device where writes will be directed too." echo "Size is specified in MB, you will be able to write that much change to the device created." echo "Prefix will get prepended to all devices created by this script in /dev/mapper" exit -1 fi MRODATA=$PREFIX${RODATA#/dev/}data COWFILELOOP=$(losetup -f) MCOWFILE=$PREFIX${RODATA#/dev/}cow MSNAPSHOT=$PREFIX${RODATA#/dev/}snap dd if=/dev/zero of=$COWFILE bs=1M seek=$FSIZE count=1 losetup $COWFILELOOP $COWFILE echo "0 $(blockdev --getsz $RODATA) linear $RODATA 0" | dmsetup create $MRODATA echo "0 $(blockdev --getsz $COWFILELOOP) linear $COWFILELOOP 0" | dmsetup create $MCOWFILE echo "0 $(blockdev --getsz /dev/mapper/$MRODATA) snapshot /dev/mapper/$MRODATA /dev/mapper/$MCOWFILE p 64" | dmsetup create $MSNAPSHOT echo "You can now use $MSNAPSHOT for your tests, up to ${FSIZE}MB." exit 0 > --Bart > -- 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
