I first read about on-line Software RAID reshaping a year ago on LWN. Today I tried it on a live system (that's too big to be backed-up first :-))
I added 2 250GB drives to my existing RAID5 array of 4, making for a 1.2TiB array. The reshape took a while...:
But when it was done:
This is one of the reasons why I love software RAID, while you have a kak load more I/O through the PCI(E) bus than you would with hardware RAID, you get the flexibility of the highest-end hardware controllers on a normal PC motherboard.
And of course, should things go pear-shaped, I don't need to find an identical controller, I just have to find a box with 6 SATA sockets.
Lets say you have 4 SATA drives,
/dev/sdd, and you are adding a new one
Check that everything is happy:
Partition the new drive (clone
sdas partition table onto
Add the new drive:
Grow the RAID:
Watch the progress:
Grow the filesystem:
See the extra space: