Why fdisk creating partition with sector 32768 and not with 2048?

Environment

• Red Hat Enterprise Linux (RHEL) 6.6
• fdisk
• parted

Issue

• Why fdisk creating partition with sector 32768 and not with 2048?

Disk /dev/sda: 2147.5 GB, 2147483648000 bytes
255 heads, 63 sectors/track, 261083 cylinders, total 4194304000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 16384 bytes / 16777216 bytes
Disk identifier: 0x162a0cbc

                       Device Boot      Start         End      Blocks   Id  System
/dev/sda1           32768  4194303999  2097135616   83  Linux

Resolution

• This is expected behavior for disk which is advertising an optimal IO size of 16777216.

Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 16384 bytes / 16777216 bytes

16777216 / 512 = 32768

Root Cause

fdisk is designed in such way that new partition is properly aligned with disk io size to avoid performance impact. In this scenario, disk optimal size is 16777216. Depending upon this optimal IO size, it will select sector offset which is (optimal_io_size/sector_size).

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