When partitioning disks larger than 2 TB on Linux, you usually need to use parted instead of fdisk. If you are used to accepting the defaults in fdisk, parted can feel a bit less forgiving.
If you insert a new disk and it appears as /dev/sdb, you can start partitioning with:
1 | parted /dev/sdb |
Inside parted, you may see an error like this:
1 | Error: /dev/sdb: unrecognised disk label |
That simply means the disk does not have a partition table yet. For disks larger than 2 TB, use GPT. For smaller disks, the traditional msdos label is usually enough:
1 | mklabel gpt |
To create a partition in parted, use mkpart. This command creates one partition across the whole disk:
1 | mkpart primary 0 100% |
The parameters mean: primary partition, starting sector, and percentage of disk space used.
That looks fine, but if you accept everything by default, you may end up with this warning:
1 | Warning: The resulting partition is not properly aligned for best performance. |
It is only a warning, but since it affects performance, it is worth fixing. The usual cause is that the starting sector is not aligned properly.
To calculate a better starting sector, check these values:
1 | cat /sys/block/sdb/queue/optimal_io_size |
If optimal_io_size is not 0, add optimal_io_size and alignment_offset, then divide by physical_block_size. In the example above:
1 | (1048576 + 0) / 512 = 2048 |
If optimal_io_size is 0, using the common default start sector 2048 is usually a good choice.
Then create the partition like this:
1 | mkpart primary 2048s 100% |
Do not forget the s suffix after 2048.
With that starting sector, the partition should be created without the alignment warning.
Reference:
http://rainbow.chard.org/2013/01/30/how-to-align-partitions-for-best-performance-using-parted/
