7.6.2.1. Linux Virtual Machines

To check the partition alignment in a Linux virtual machine, log in to this virtual machine and run the following command:

# fdisk -l -u /dev/device_name

For example, to check the partition alignment on the sdc device, you can run this command:

# fdisk -l -u /dev/sdc
Disk /dev/sdc: 73.0 GB, 73014444032 bytes
255 heads, 63 sectors/track, 8876 cylinders, total 142606336 sectors
Units = sectors of 1 * 512 = 512 bytes
   Device       Boot    Start         End       Blocks  Id      System
/dev/sdc1       *          63      208844       104391  83      Linux
/dev/sdc2              208845   142592939    71192047+  8e      Linux LVM

Pay attention to the number of sectors in the Start column. Usually, a sector contains 512 bytes, which makes up 32256 bytes for 63 sectors for the /dev/sdc1 partition and 26105625 bytes for 208845 for the /dev/sdc2 partition. For a partition to be properly aligned, it must align with 4096 byte boundaries (assuming that the block size of your storage is 4 KB). As 32256 and 106928640 is not a multiple of 4096, the partitions /dev/sdc1 and /dev/sdc2 are not aligned properly. To align them, you should offset

  • the /dev/sdc1 partition by 1 sector so that it starts at 64. In this case, 64 sectors each containing 512 bytes make up 32768 that is a multiple of 4096.
  • the /dev/sdc2 partition by 3 sectors so that it starts at 208848. In this case, 208848 sectors each containing 512 bytes make up 106930176 that is a multiple of 4096.
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