On Fri, 8 Aug 2014 18:46:52 +0200 mdraid.pkoch@xxxxxxxx (Peter Koch) wrote: > Dear Neil, > > thanks for the info about set meaning of set-A, the difference > between Device-ID and RaidDevice. > > > > Number Major Minor RaidDevice State > > > 0 8 16 0 active sync set-A /dev/sdb > > > 1 8 160 1 active sync set-B /dev/sdk > > > 2 8 32 2 active sync set-A /dev/sdc > > > 3 8 176 3 active sync set-B /dev/sdl > > > 4 8 48 4 active sync set-A /dev/sdd > > > 5 8 192 5 active sync set-B /dev/sdm > > > 6 8 64 6 active sync set-A /dev/sde > > > 7 8 208 7 active sync set-B /dev/sdn > > > 8 8 80 8 active sync set-A /dev/sdf > > > 9 8 224 9 active sync set-B /dev/sdo > > > 10 8 96 10 active sync set-A /dev/sdg > > > 11 8 240 11 active sync set-B /dev/sdp > > > 12 8 112 12 active sync set-A /dev/sdh > > > 14 8 128 13 active sync set-B /dev/sdi > > > 13 65 0 14 active sync set-A /dev/sdq > > > 15 65 16 15 active sync set-B /dev/sdr > > > > It's not "sync set-A", it is "active" and "sync" and "set-A". > > When you have a RAID10 that can be seen as two sets of devices where one set > > is mirrored to the other, they are labels as "set-A" and "set-B", just like > > you assumed. > > The first time I noticed "set-A" and "set-B" in mdadm -D output > was after the reshape operation started. If I understand you > correct the real reason for these information to appear was not > the reshape operation but growing the array from an odd number > of drives (13) to an even number (16) Correct. A 13 drive array would not have well defined sets. > > > > What's the difference between column 1 and column 4 in > > > mdadm -D output? > > > > column 1 identified the device. column 4 give the role that the device plays > > in the array. > > This seemed to make sense once, but it could be more confusing than helpful. > > What irritates me most is the fact that /proc/mdstat output > lists the device id. For a raid10-array with near-2 layout and > an even number of drives I was under the impression that the data > is mirrored between all drives with even and all drives with odd > numbers. In my case this is wrong: drives 0,2,4,6,8,10,12,13 > are mirrored with drives 1,3,5,7,9,11,14,15. Yes, that irritates me too. I haven't quite managed to work up the courage to "fix" it as technically it is an API change and someone might depend on the current behaviour. > > Spare-Drives are not shown with their number but with their role > within the array (namely (S) ). So why not printing the role > for all drives instead of their device-id. I would also suggest > adding the set to mdstat-output, i.e: > > md5 : active raid10 sdb[A0] sdr[B7] sdq[A7] sdi[B6] sdh[A6] sdp[B5] sdg[A5] sdo[B4] sdf[A4] sdn[B3] sde[A3] sdm[B2] sdd[A2] sdl[B1] sdc[A1] sdk[B0] > That would be an even bigger API change. I have seriously considered writing an mdadm comment which prints out a summary similar to /proc/mdstat, but with a better thought out structure and content. Then I could just tell people to ignore mdstat. I haven't yet. > Is there any way to change the device-id? If you --zero the superblock, then add the device again, it might get a different device id. NeilBrown
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