On Wed, 10 Aug 2011 00:12:04 +0200 Michal Soltys <soltys@xxxxxxxx> wrote: > Hi > > I've been doing some tests, mostly for "what would happen if" scenarios > of incremental / foreign metadata assembly - as I avoid those if > possible, still a few things I noticed: Great!! Tests are good - especially testing things that I wouldn't think of :-) > > 1) > > With native metadata, 'mdadm -IRs' can be used to force-run partially > assembled arrays. With external metadata (tested with ddf) though, the > command has no effect. The subarray can be forced into degraded / active > mode through regular 'mdadm -R' - though it also requires manual start > of mdmon (otherwise further operations might end in D state, until the > one is started). For example: > > mdadm -C /dev/md/ddf0 -e ddf -n4 /dev/sd[b-e] > mdadm -C /dev/md/test -l5 -n4 /dev/md/ddf0 > mdadm -S /dev/md/test /dev/md/ddf0 > > mdadm -I /dev/sdb > mdadm -I /dev/sdc > mdadm -I /dev/sdd > mdadm -R /dev/md/test > > At this point, if the remaining component is added, e.g. > mdadm -I /dev/sde > > Then mdmon will have to be started, or any process trying to write will > hang (though mdmon can be started at any moment). > > So in short: > > - shouldn't -IRs also consider foreign metadata subarrays ? It should. A quick look at the code suggests that it does. So there is clearly a bug somewhere. I've added it to my list of things to fix. > - shouldn't mdmon be started automatically for run-forced subarrays ? Definitely. That code is simply missing. I've added that to my list too. > > 2) mixing 'mdadm -I' and 'mdadm -As' > > If part of an array (possibly runnable) is assembled through 'mdadm -I', > and then 'mdadm -As' is called, it will cause creation of a duplicate > array from the remaining disks. This was true for both native and > external metadata formats. For example: > > mdadm -C /dev/md/ddf0 -e ddf -n4 /dev/sd[b-e] > mdadm -C /dev/md/test -l1 -n4 /dev/md/ddf0 > mdadm -S /dev/md/test /dev/md/ddf0 > > mdadm -I /dev/sdb > mdadm: container /dev/md/ddf0 now has 1 devices > mdadm: /dev/md/test assembled with 1 devices but not started > > mdadm -I /dev/sdc > mdadm: container /dev/md/ddf0 now has 2 devices > mdadm: /dev/md/test assembled with 1 devices but not started > > mdadm -As > mdadm: Container /dev/md/ddf1 has been assembled with 2 drives (out of 4) > mdadm: /dev/md/test_0 assembled with 2 devices but not started > > At this point, there're 2 containers + 2 subarrays created, both of > which can be started with 'mdadm -R' to operate independently: > > md124 : active raid1 sdd[1] sde[0] > 13312 blocks super external:/md125/0 [4/2] [__UU] > > md125 : inactive sdd[1](S) sde[0](S) > 65536 blocks super external:ddf > > md126 : active raid1 sdc[1] sdb[0] > 13312 blocks super external:/md127/0 [4/2] [UU__] > > md127 : inactive sdc[1](S) sdb[0](S) > 65536 blocks super external:ddf > > > I realize that mixing normal and incremental assembly is at least asking > for problems, though I don't know if the above results fall into "bug" > or "don't do really weird things" scenario. This sounds very familiar. I thought I had fixed something similar to that recently... If you have two halves of a RAID1 that both look OK but the event counts are too different, then the first "mdadm -As" would build an md/raid1 with just one of them, then another "mdadm -As" would build an md/raid1 with just the other - clearly not what you want, but very similar to what you have. But I cannot find any evidence that I fixed it. So I've added this to my list too. I don't know when I'll get to working on this list, but hopefully within a month or 2 :-) Thanks a lot for the report (and sorry for the delay in replying). NeilBrown > -- > 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
