[Bug 794963] Re: madam allows growing an array beyond metadata size limitations

[slith]

I probably should have mentioned that the command to grow after
replacing each of the siz 2TB HDDs with 3TB HDDs one-by-one, I used the
following command to grow the array:

sudo mdadm --grow --size=max /dev/md1

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Title:
  madam allows growing an array beyond metadata size limitations

Status in “mdadm” package in Ubuntu:
  New

Bug description:
  Binary package hint: mdadm

  It is possible to command mdadm to grow an array such that the array space on a component partition exceeds the maximum size writeable in metadata 0.90 format, which is just over 2TB (4 bytes representing sector size).  When told to do this, mdadm appears to do it without error and writes a bogus sector count into the 4 byte container in the super-blocks. Now the system operates with the over-enlarged array without apparent issue but only until the next reboot when the system is told the array size based on the superblock value. User data becomes inaccessible/LVMs don't mount with seemingly no way to recover the inaccessible data.
  Obviously, mdadm should refuse to grow the array size beyond the size restriction of its own metadata.
  Seen using mdadm - v2.6.7.1 - 15th October 2008 and Ubuntu server 10.04 64-bit

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