Used Dev Size is wrong

[Bart Kus <me@bartk.us>]

Hello RAID gurus,

I recently upgraded my MD 10x1TB RAID6 to a 10x2TB RAID6.  I did this by 
replacing all the 1TB drives in the array with 2TB drives, no more than 
2 at a time, and letting the array rebuild to assimilate the fresh 
drive(s).  The array finished its last rebuild and showed an Array Size 
of 8000GB, and a Used Dev Size of 2000GB.  Since this isn't the 16TB I 
was looking for, I went through a grow operation:

# mdadm /dev/md4 -G -z max

This started a resync @ 50% complete and continued from there.  This had 
the expected effect of increasing the reported Array Size to 16000GB, 
but it also unexpectedly increased the Used Dev Size to 4000GB!  I'm 
worried this incorrect size will lead to errors down the road.  What can 
I do to correct this?  Here are the details of the case:

jo dev # cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4]
md4 : active raid6 sdl1[13] sdj1[19] sdg1[18] sdd1[17] sdf1[16] sdc1[15] 
sdi1[14] sde1[12] sdk1[11] sdh1[10]
      15628094464 blocks super 1.2 level 6, 64k chunk, algorithm 2 
[10/10] [UUUUUUUUUU]
      [===========>.........]  resync = 55.6% (1087519792/1953511808) 
finish=342.1min speed=42184K/sec

# mdadm --detail /dev/md4
/dev/md4:
        Version : 1.02
  Creation Time : Sun Aug 10 23:41:49 2008
     Raid Level : raid6
     Array Size : 15628094464 (14904.11 GiB 16003.17 GB)
  Used Dev Size : 3907023616 (3726.03 GiB 4000.79 GB)
   Raid Devices : 10
  Total Devices : 10
Preferred Minor : 4
    Persistence : Superblock is persistent

    Update Time : Sun Oct 25 09:07:29 2009
          State : active, resyncing
 Active Devices : 10
Working Devices : 10
 Failed Devices : 0
  Spare Devices : 0

     Chunk Size : 64K

 Rebuild Status : 55% complete

           Name : 4
           UUID : da14eb85:00658f24:80f7a070:b9026515
         Events : 2901293

    Number   Major   Minor   RaidDevice State
      15       8       33        0      active sync   /dev/sdc1
      14       8      129        1      active sync   /dev/sdi1
      12       8       65        2      active sync   /dev/sde1
      16       8       81        3      active sync   /dev/sdf1
      17       8       49        4      active sync   /dev/sdd1
      18       8       97        5      active sync   /dev/sdg1
      10       8      113        6      active sync   /dev/sdh1
      19       8      145        7      active sync   /dev/sdj1
      11       8      161        8      active sync   /dev/sdk1
      13       8      177        9      active sync   /dev/sdl1

# uname -a
Linux jo.bartk.us 2.6.29-gentoo-r5 #1 SMP Fri Jun 19 23:04:52 PDT 2009 
x86_64 Intel(R) Pentium(R) D CPU 2.80GHz GenuineIntel GNU/Linux

# mdadm --examine /dev/sdc1
/dev/sdc1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : da14eb85:00658f24:80f7a070:b9026515
           Name : 4
  Creation Time : Sun Aug 10 23:41:49 2008
     Raid Level : raid6
   Raid Devices : 10

 Avail Dev Size : 3907023730 (1863.01 GiB 2000.40 GB)
     Array Size : 31256188928 (14904.11 GiB 16003.17 GB)
  Used Dev Size : 3907023616 (1863.01 GiB 2000.40 GB)
    Data Offset : 272 sectors
   Super Offset : 8 sectors
          State : active
    Device UUID : 56d9fdeb:5170f643:5d4c4a2b:b656838a

    Update Time : Sun Oct 25 09:07:29 2009
       Checksum : c8785262 - correct
         Events : 2901293

     Chunk Size : 64K

    Array Slot : 15 (failed, failed, failed, failed, failed, failed, 
failed, failed, failed, failed, 6, 8, 2, 9, 1, 0, 3, 4, 5, 7)
   Array State : Uuuuuuuuuu 10 failed

# fdisk /dev/sdc

The number of cylinders for this disk is set to 243201.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/sdc: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x3a18d025

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1      243201  1953512001   fd  Linux raid 
autodetect


Thanks in advance for your help!

--Bart