vSphere Storage and vSAN
Storage abstractions
Datastores are backed by VMFS, NFS (3 or 4.1), vVols, or vSAN. Block storage reaches the host through FC, FCoE, iSCSI (software or dependent hardware adapter), or NVMe over Fabrics. Storage Policies (SPBM) describe requirements such as failures to tolerate, stripe width, and provisioning type, and are applied per VM disk.
Multipathing and integration
Pluggable Storage Architecture components include the NMP/HPP, SATP (array rules) and PSP (fixed, most recently used, round robin). Round robin defaults to switching paths every 1000 I/Os per device unless a rule changes it. VAAI offloads clone, zero and lock operations to compliant arrays. SIOC throttles noisy neighbors; Storage DRS balances datastores in a datastore cluster.
vSAN essentials
vSAN is software-defined, policy-driven storage built from host local disks. Original Storage Architecture uses disk groups with cache and capacity tiers; Express Storage Architecture uses NVMe and pools devices without disk groups. Resilience comes from FTT and RAID-1/RAID-5/RAID-6, with a witness host for stretched clusters. Deduplication and compression, encryption, and vSAN health checks are common exam topics.
Traps
iSCSI port binding requires a dedicated VMkernel adapter bound to the software adapter. NFS 4.1 adds Kerberos, multipathing and session trunking that NFS 3 lacks. vSAN RAID-5 needs at least four hosts and RAID-6 at least six. ESA has no disk groups and has different hardware requirements than OSA.
Rule of thumb
When a performance question appears, first ask whether the problem is path-level (multipathing), array-level (VAAI), or contention-level (SIOC) before recommending a storage policy change.