I recently changed the disks in my RAID5 from 3x2TB to 3x3TB. I also wanted to change the chunk size from default 512k to 128k. I have added all new devices to the array and I run:
mdadm /dev/md1 --grow --backup-file=/boot/md1_grow_backup_file --chunk=128
The --backup-file option is necessary because of the chunk size change and the file specified by it is on a different block device.
I have to shutdown the server to physically move it, but the reshape operation is going much slower than I anticipated, so I'm wondering if I can interrupt the process and continue it after reboot.
The manpage has some information on interrupting the --grow/reshape process, but it seems to me that this was meant to cover some catastrophic circumstances - loss of power, server lockup, etc.
Is it possible to gracefully stop a mdadm array reshape? If so, how to stop the array and how to resume the reshape after booting? Will the backup file be necessary?