Flash endurance is related to the number of write/erase cycles that the cache-tier flash SSD can tolerate over its lifespan. It is important to choose the right level of endurance for each application or use case, according to the level of write activity that is expected.
For vSAN and VxRail configurations, the endurance specification uses Terabytes Written per day (TBW) as a metric to determine endurance.
For all-flash vSAN deployments, the specification for the cache device is 4TBW per day, which is an appropriate endurance for write intensive workloads.
There are two commonly used approaches to improve NAND flash endurance: improve wear leveling and minimize write activity. A distributed storage implementation that focuses on localizing data on the same node where the VMs reside prevents the distribution of the writes across all the drives in the cluster. This localization inevitably increases drive usage, leading to early drive replacement.
In contrast, vSAN distributes the objects and components of a VM across all the disk groups in the VxRail cluster. This distribution significantly improves wear leveling and reduces write activity by deferring writes. vSAN also reduces writes by employing data-reduction techniques such as de-duplication and compression.