vSAN Performance is degraded when I/Os are not 4k aligned
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vSAN Performance is degraded when I/Os are not 4k aligned


Article ID: 326867


Updated On:


VMware vSAN


This KB is written to inform of this known limitation and provide resources to implement known workarounds and solutions.

vSAN Performance is less than expected with possible higher latency and lower throughput coupled with I/O sizes issued that are not 4k aligned.


VMware vSAN


vSAN is designed to work best with 4k aligned I/O (4k, 8k, 16k, 32k, 64k, etc) from guests. When I/O is not aligned to a 4k size, additional I/O operations are required at the vSAN layer before the write can be completed. This adds time (latency) until these operations are completed.

You may use I/O Insight to determine if non-alignment is a factor by looking at the I/O patterns of specific VMs.


Ensure that the guest operating system and applications are set to use 4k blocks for all I/O operations. Engage your application team/software vendor to ensure the OS/application is using 4k blocks and if not configure the I/O for 4k block size.

Additional Information

Information regarding 512e & 4k native drives: https://kb.vmware.com/s/article/2091600

Any changes at the guest operating system or application should be discussed with the relevant vendor of the respective vendor.