Optimise Oracle VM 3.x Oracle Linux guest write I/O performance through guest/host partition boundary alignment (Doc ID 1632576.1)

Last updated on AUGUST 14, 2017

Applies to:

Oracle VM - Version 3.1.1 and later
Linux x86-64

Symptoms

Oracle Linux 6 (and lower) guest Virtual Machines (VMs) running on Oracle VM 3.x may experience suboptimal write I/O performance to virtual disk filesystems/partitions.

Following is an example of fdisk(8) and parted(8) output from an Oracle VM 3.2 OL5.10 guest (GUEST1-UNALIGNED) with default, unaligned created partitions:

The table data above denotes that writes to aligned partition /dev/xvda7 consistently performed better than to any/all other unaligned partitions.
Best case, writes to aligned device /dev/xvda7 (11.4Mb/s) saw ~120% increase in throughput compared to the worst observed write performance to unaligned devices (5.2Mb/s)
Worst case, writes to aligned device /dev/xvda7 (10.8Mb/s) saw ~30% increase in throughput compared to the best observed write performance to unaligned devices (8.3Mb/s)

Cause

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