OK, I think I am even closer still, but not yet. I found the --layout=
parameter which can take the values: ddf-zero-restart, ddf-N-restart,
and ddf-N-continue, and I am pretty sure this needs to be issued against
the RAID array itself, not the container. I am still not sure which of
the layout parameters should be employed, but there seems to be a bigger
issue. The array needs to have a missing (4th) member, but I can't get
this to work:
RAID-Server:/RAID/Server-Main/Temp# mdadm --create /dev/md70
/dev/loop[0-2] missing --raid-devices 4 --metadata=ddf
...
mdadm: This level does not support missing devices
RAID-Server:/RAID/Server-Main/Temp# mdadm --create /dev/md70
/dev/loop[0-2] -n 4 --metadata=ddf
mdadm: You haven't given enough devices (real or missing) to create this
array
RAID-Server:/RAID/Server-Main/Temp# mdadm --create /dev/md70
/dev/loop[0-2] -n 3 --metadata=ddf
...
mdadm: container /dev/md70 prepared.
RAID-Server:/RAID/Server-Main/Temp# cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4]
md70 : inactive loop2[2](S) loop1[1](S) loop0[0](S)
98304 blocks super external:ddf
RAID-Server:/RAID/Server-Main/Temp# mdadm --create /dev/md7 /dev/md70
missing -n 4 -l 5 -p ddf-N-restart
mdadm: You haven't given enough devices (real or missing) to create this
array
I don't know what to try next. If I specify --raid-devices=3 for
the array, it will take it to be a 2 drive + parity array, not a 3 drive
+ 1 missing with parity array. Is there a way to add a missing drive to
the DDF container? Is there a way to create the DDF container with a
4th (phantom) drive and then delete the drive?
On 1/30/2019 8:37 PM, Leslie Rhorer wrote:
I did some research, and I think I am getting a bit closer. The
information is a bit cryptic, but if I understand correctly, first I
need to set up a DDF Container. I think the command should be:
mdadm --create /dev/md70 /dev/loop[0-2] missing --raid-devices 4
--metadata=ddf-????
I'm not sure what the metadata parameter should be, however, or
how to find out. The MAN page only lists ddf as a proper metadata
style. The superblock is definitely at the end of the RAID members. To
me this suggests a V0.9 or 1.0 superblock. Mdadm reports version
01.00.00, but that is a different format from the my v1.2 arrays.
Then as I understand it, I need to create a member array:
mdadm --create /dev/md7 /dev/md70 --raid-devices 4 --level 5
--chunk=512(?)
I think the chunk size should be 512, right? Mdadm reports the
chunk size to be 1024 sectors, but the sectors are 512 bytes, so 1024
sectors would be 512KB. Should the chunk size be specified for the
container, as well, or perhaps only the container?
