VMware vSAN OSA and ESA Algorithm overview
VMware vSAN's Original Storage Architecture (OSA) uses a two-tier model with disk groups, while the newer Express Storage Architecture (ESA), introduced in vSAN 8, utilizes a single-tier model with a log-structured file system optimized for modern, high-performance NVMe storage. Original Storage Architecture (OSA) Overview The OSA was designed to be compatible with a wide range of hardware, including hybrid (flash cache, spinning disk capacity) and all-flash configurations. Two-Tier Model: It separates storage devices into distinct cache and capacity tiers organized into disk groups. Disk Groups: Each disk group has one flash device for caching and buffering writes (and reads in hybrid configurations) and one to seven devices for persistent capacity. Data Flow & Processing: Writes are first sent to the high-performance cache tier (write buffer) and acknowledged quickly to the VM. Data is then "destaged" to the capacity tier in a process that involves a read-modify-w...