On Tue, 19 Mar 2013 19:29:44 +0100 Martin Wilck <mwilck@xxxxxxxx> wrote: > On 03/18/2013 12:35 AM, NeilBrown wrote: > > > With -R, it only stays inactive until we have the minimum devices needed for > > a functioning array. Then it will switch to 'read-auto' or, if the array is > > known and all expected devices are present, it will switch to 'active'. > > That's the point - I see the array switch to active *before* all > expected devices are present. That causes further additions to fail. > > > Maybe if you could provide a sequence of "mdadm" commands that produces an > > outcome different to what you would expect - that would reduce the chance > > that I get confused. > > Here is the sequence of mdadm commands to illustrate what I mean. > I have a RAID10 array and I add the devices using mdadm -I -R in the > sequence 1,3,2,4. After adding device 3, the array will be started in > auto-read-only mode, which is fine. > > But then as soon as the next disk (/dev/tosh/rd2) is added, the array > switches to "active" although it is neither written to, nor all disks > have been added yet. Consequently, adding disk 4 fails. > > I expected the array to remain "auto-read-only" until either all 4 > devices are present, or it is opened for writing. This is how the > container case is behaving (almost - it doesn't switch to active > automatically until it's written to). > > # ./mdadm -C /dev/md0 -l 1 -n 4 /dev/tosh/rd[1-4] -pn2 > mdadm: array /dev/md0 started. > (wait for initial build to finish) > # mdadm -S /dev/md0 > mdadm: stopped /dev/md0 > # ./mdadm -v -I /dev/tosh/rd1 -R > mdadm: /dev/tosh/rd1 attached to /dev/md/0, not enough to start (1). > # ./mdadm -v -I /dev/tosh/rd3 -R > mdadm: /dev/tosh/rd3 attached to /dev/md/0, which has been started. > # cat /proc/mdstat > Personalities : [raid1] [raid10] > md0 : active (auto-read-only) raid10 dm-6[2] dm-4[0] > 2094080 blocks super 1.2 512K chunks 2 near-copies [4/2] [U_U_] > # ./mdadm -v -I /dev/tosh/rd2 -R; cat /proc/mdstat > mdadm: /dev/tosh/rd2 attached to /dev/md/0 which is already active. > Personalities : [raid1] [raid10] > md0 : active raid10 dm-5[1] dm-6[2] dm-4[0] > 2094080 blocks super 1.2 512K chunks 2 near-copies [4/2] [U_U_] > [>....................] recovery = 0.0% (0/1047040) > finish=1090.6min speed=0K/sec > (wait for recovery to finish) > # ./mdadm -v -I /dev/tosh/rd4 -R > mdadm: can only add /dev/tosh/rd4 to /dev/md/0 as a spare, and > force-spare is not set. > mdadm: failed to add /dev/tosh/rd4 to existing array /dev/md/0: Invalid > argument. > > Thanks, > Martin Thanks, that makes is all very clear. The problem is that the ADD_NEW_DISK ioctl automatically converts from read-auto to active. There are two approaches I could take to addressing this. 1/ change ADD_NEW_DISK to not cause that conversion. I think that would need to be conditional as some times it really should be changed. 2/ change mdadm to not use ADD_NEW_DISK but instead add the disk my setting it up via sysfs. I'm not sure which is best and neither is completely straight forward. So for now: I'll get back to you. Thanks, NeilBrown
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