Dear Adam
On 10/26/2015 10:26 AM, Adam Goryachev wrote:
1) fail two drives from the array:
mdadm --manage /dev/md0 --fail /dev/sdb1
mdadm --manage /dev/md0 --remove /dev/sdb1
mdadm --manage /dev/md0 --fail /dev/sdd1
mdadm --manage /dev/md0 --remove /dev/sdd1
mdadm --misc --zero-superblock /dev/sdb1
mdadm --misc --zero-superblock /dev/sdd1
It seems that RAID10 device number is in order:
sdb1 device0
sdc1 device1
sdd1 device2
sde1 device3
Therefore, I can fail device 0 (sdb1) and device 2 (sdd1) without losing
any data.
2) create a 3 disk RAID5 with one disk missing.
mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sdb1 /dev/sdd1
missing
3) Then copy all of the existing data across
unmount partitions, stop LVM/etc
dd bs=16M if=/dev/md0 of=/dev/md1
I dont know why this would be necessary.
4) Finally, stop the md0, and add the two devices to the new raid5, and
then grow the array to use the space on the 4th drive.
mdadm --manage --stop /dev/md0
mdadm --misc --zero-superblock /dev/sdc1
mdadm --manage /dev/md1 --add /dev/sdc1
mdadm --misc --zero-superblock /dev/sde1
mdadm --manage /dev/md1 --add /dev/sde1
mdadm --grow /dev/md1 --raid-devices=4
5) Add the space to my LVM
pvresize /dev/md1
6) Start up LVM, mount LV's, etc
I tried your method on a local system, and it seemed to worked.
The reason why I said that dd would'nt be necessary, as it is raid
syncing would work. You just need to be careful that you should not
start doing remove/add and other changing aspects of raid till the time
syncing is going on.
Finally when you grow your raid in RAID5 also syncing would happen.
Regards
Anugraha Sinha
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