RAID5 losing initial synchronization on restart when one disk is spare

[Hubert Verstraete <hubskml@xxxxxxx>]

Hello

According to mdadm's man page:
"When creating a RAID5 array, mdadm will automatically create a degraded
array with an extra spare drive. This is because building the spare
into a degraded array is in general faster than resyncing the parity on
a non-degraded, but not clean, array. This feature can be over-ridden
with the --force option."

Unfortunately, I'm seeing a kind of bug when I create a RAID5 array with 
an internal bitmap, then stop the array before the initial 
synchronization is done and restart the array.

1° When I create the array with an internal bitmap:
mdadm -C /dev/md_d1 -e 1.2 -l 5 -n 4 -b internal -R /dev/sd?
I see the last disk as a spare disk. After the restart of the array, all 
disks are seen active and the array is not continuing the aborted 
synchronization!
Note that I did not use the --assume-clean option.

2° When I create the array without a bitmap:
mdadm -C /dev/md_d1 -e 1.2 -l 5 -n 4 -R /dev/sd?
I see the last disk as a spare disk. After the restart of the array, the 
spare disk is still a spare disk and the array continues the 
synchronization where it had stopped.

In the case 1°, is this a bug or did I miss something?
Secondly, what could be the consequences of this non-performed 
synchronization ?

Kernel version: 2.6.26-rc4
mdadm version: 2.6.2

Thanks,
Hubert
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