Last blogpost was on vSAN ESA, so it makes good sense to now look at OSA.
OSA stands for Original Storage Architecture. This design provides a two-tier architecture with caching and capacity tiers. It is the original architecture, and it is supported within all versions of vSAN. ESA is only supported in version 8. You cannot upgrade an OSA to ESA; the latter has to be built new from scratch.
The advantage of OSA is that it is non-hardware specific. Each HCI node has two sets of disks: a high-performance disk for cache and a disk group for capacity. The capacity disk groups can be high-performance or spinning drives.
OSA vs. ESA: Just because a new shiny version is out doesn’t make the old one bad. The ESA direction has several hardware requirements, which may not make it the best solution for all organizations.
A potential downside of the OSA is the Single Point of failure with the Cache Drive. The whole disk group it supports on the given host will become unavailable if it fails.
With OSA, the Write operations are stored in the Cache drives and offloaded to the capacity drives. All read operations take place from the Capacity drives.
