Parted, optimal aligment

SYMPTOMS

When you labble and create partion on disk, parted say you something like this

(parted) mklabel gpt
(parted) mkpart primary 0 100%
Warning: The resulting partition is not properly aligned for best performance.
Ignore/Cancel?

SOLUTION

Get the alignment parameters for your array (remember to replace sdb with the name of your device as seen by the kernel).

# cat /sys/block/sdb/queue/optimal_io_size
1048576
# cat /sys/block/sdb/queue/minimum_io_size
262144
# cat /sys/block/sdb/alignment_offset
0
# cat /sys/block/sdb/queue/physical_block_size
512

Add optimal_io_size to alignment_offset and divide the result by physical_block_size. In my case this was (1048576 + 0) / 512 = 2048.

This number is the sector at which the partition should start. Your new parted command should look like:

mkpart primary 2048s 100%

The trailing ‘s’ is important: it tells parted that you’re talking about sectors, not bytes or megabytes.