ADR-057: VMFS datastore layout, not vVol
Date: 2026-02-21 Status: Accepted
Context
Dell PowerStore supports two VMware storage paradigms:
| Feature | VMFS Datastores | vVol Datastores |
|---|---|---|
| Snapshot granularity | Volume-level (all VMs) | Per-VM via VASA |
| QoS | Per-volume | Per-VM (SPBM) |
| Operational maturity | Very mature | Newer, fewer admins |
| Backup tool support | Universal | Growing but incomplete |
| Dell recommendation | Supported | Preferred for new deployments |
Dell's own documentation recommends vVols for new deployments. However, the practical reality for migration projects is different: most customers migrating from legacy arrays (VNX2, SC Series, Unity) have VMFS datastores today and will continue using VMFS on PowerStore.
Decision
The layout engine generates VMFS datastore recommendations only. vVol layout is out of scope.
Rationale:
- Migration continuity: Customers moving from legacy → PowerStore keep VMFS. Proposing vVol adds a second migration dimension (storage paradigm change) that complicates the project.
- Snapshot/backup implications matter: VMFS volume-level snapshots make datastore layout directly impactful for RPO/RTO. With vVols, per-VM snapshots make layout less critical — the engine's value proposition is weaker.
- SDRS/SIOC deprecation: VMware deprecated SDRS I/O balancing and SIOC in vSphere 8.0 U3 (June 2024). This means VMFS layouts can no longer rely on automatic I/O rebalancing, making manual layout planning (what our engine does) more valuable than ever.
- Pre-sales reality: The target user is proposing a migration, not a greenfield deployment. VMFS is what they'll present to the customer.
Consequences
- The layout engine operates in terms of VMFS datastores (volumes), not vVol storage containers.
- Snapshot granularity ratings in comparison metrics are meaningful because VMFS snapshots are volume-scoped.
- A future version could add vVol recommendations as a fourth strategy or a separate mode, but this is deferred.