Thanks for the quick reply Neil,

I tried the suggested syntax, excluding the array-size in order to
have mdadm give me the value - but it did not.  I also tried grabbing
the current array size from df, but I got an error about being unable
to change array size in the same operation.

So just to confirm I'm understanding you correctly ;  mdadm -G
/dev/md127 --raid-devices 5 --backup=/root/backup  - should generate
an error that provides the array-size value?

On Thu, May 20, 2010 at 3:34 PM, Neil Brown [off-list ref] wrote:

On Thu, 20 May 2010 07:45:23 -0600
"Keith ." [off-list ref] wrote:

quoted

Does mdadm 3.1.x not support shrinking the number of disks in a RAID5 array?

I have successfully converted my 6x1.5tb RAID6 array to a 6x1.5tb
RAID5 array.  The issue that I now face is that one of those 6 drives
is failed / removed, and as a result - the new RAID5 array is down
it's parity drive.

I knew I was short a disk when I started the process, but I was under
the assumption that mdadm now supported shrinking of RAID5/6 arrays.
Am I mistaken, or can anyone throw some suggestions at me so I can
give it a try?

It should work.

 mdadm -G /dev/mdX --raid-devices 5 --array-size=XXXXX
 --backup=/root/backup-file

If you don't give the 'array-size' value mdadm will tell you what it has to
be.  You need to be sure that all your data is already within that space.

NeilBrown

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