Growing a RAID6 array on 11.10 *** SOLVED ***

Steven Davies-Morris sdavmor at
Fri Mar 9 00:09:07 UTC 2012

On 03/07/2012 02:49 PM, Steven Davies-Morris wrote:
> I have two RAID arrays on a system. The first is RAID1 and supports
> /boot, swap / and /home. The second is RAID6 and supports everything
>  else. It currently has 4 3TB drives. I have 3 more sitting in the
> tower and want to add them to the RAID6 array.
> I was using Disk Utility to try to add these three drives but it
> doesn't seem to want to do it with the array up and running. When I
> take the array down I'm denied access to the array controls in "Edit
> Components" so I can't tell it to add drives.
> I remove the partitions from the 3 drives (initialized as GPT). Then
> I go into "Edit Components". I see the three drives. I am told they
> each have no partitions and each have 3TB available for use.
> I go to add one drive. I click the box to add it and the click
> "Expand". I authenticate then get this message:
> Error expanding RAID Array. An error occurred while performing on
> operation on "hitchcock RAID6" (6.0 TB RAID-6 Array): The operation
> failed
> Detail information says:
> Error expanding array: helper script exited with exit code 1: mdadm:
> added /dev/sdc1 mdadm: Need to backup 6144K of critical section..
> I now see the new drive in the RAID6 array as a spare.
> What am I missing here? If I can't figure this out I guess it will be
> a reboot into a run-level 1 root shell to douse mdadm. Any pointers
> from those of you who are quite familiar with using Disk Utility and
> RAID arrays?

I finally figured out what was going on. Digging further into the error
message output I kept looking at the issue of bitmap removal. Why was
this necessary? And removal from where? I had an epiphany 30 mins ago
reading this mdadm man page:


Which then led me to search online and read this page which has some
good information about speeding up working with Linux software raid:


What I wound up doing was removing the bitmap from the array with this
shell command:

sudo mdadm --grow --bitmap=none /dev/md127

I was then able to expand the array using Disk Utility, though I could
have done it from a terminal shell with this command:

sudo mdadm --grow /dev/md127 --raid-devices=7

Once I'm done with the reshaping I'll put the bitmap back after figuring
out what it should optimally be. The RAID6 array is reshaping right now
with the three new 3TB drives added. In a few hours I will seal it all
back up. In the meantime I'm off to Fry's Electronics to return the
extra pieces of hardware that I don't need.

The final configuration of the media center server will be a 8gb DDR3
machine with a AMD Phenom II X4 quad-core processor. It will have a
RAID1 mirror of 2*2TB drives for boot, swap, / and home. And 7*3TB
drives for the RAID6 array. 4 will be on the mobo along with the boot
mirror. The other 3 drives will be on a 4port SATA card. 6 drives are
mounted in the 3.5" drive bays and the other 3 plus the PATA DVD burner
are mounted in the 5.25" drive bays. 4 big fans, plus 1 giant fan and a
1200watt power-supply. Hopefully I'm now done tinkering with it and can
get back to software and music.
SDM a 21st century schizoid man in SoCal
Systems Theory website
"overfulnoisecascade" CD coming soon

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