Summary of "VMware vSAN Express Storage Architecture Components. \\ What happened to my Witness Components??"

VMware vSAN Express Storage Architecture (ESA) Overview

The video provides an in-depth explanation and demonstration of VMware vSAN Express Storage Architecture (ESA) components, focusing on the changes from the original vSAN architecture, particularly around how witness components are handled.

Key Technological Concepts and Product Features

1. Express Storage Architecture (ESA) Overview

ESA replaces traditional disk groups and cache tiers with a single storage pool.
All disks inside a server are pooled together without dedicated cache devices.
Only SSD or NVMe drives are supported.
ESA currently works only on vSAN Ready Nodes with strict hardware compatibility.
Network requirements are higher, with at least 20 Gbps recommended for production environments.

2. Component Structure in ESA

Objects (such as VM virtual disks, VM home, swap files) are composed of components.
Each object consists of two main types of components:
- Performance Leg: Handles all writes first; acts like a high-speed cache.
- Capacity Leg: Stores data long-term after the performance leg completes a full stripe.
The number of performance components depends on the failure tolerance setting (failure to tolerate + 1).

3. Failure Tolerance and RAID Types

Mirroring (RAID 1): Performance leg components mirror data across hosts for redundancy.
RAID 5: Data is striped with parity across components; more space-efficient but slower writes due to parity calculations.
RAID 6: Similar to RAID 5 but with double parity, allowing loss of two hosts; slower writes but higher fault tolerance.
ESA introduces adaptive RAID 5, allowing dynamic restriping from 3-5 hosts (2+1) to 6+ hosts (4+1), improving flexibility.
Performance legs are always mirrored (RAID 1) to avoid write penalties and ensure high write performance.

4. Witness Components in ESA

Unlike the original vSAN architecture, witness components are often not visible or necessary in ESA.
Performance legs can act as witnesses in mirroring configurations.
Witness components may appear only in specific scenarios, such as when storage capacity is constrained or placement of components is difficult.
Witnesses are used only in mirroring failure tolerance modes (FTT=1, 2, 3) and not in RAID 5 or RAID 6.
The presenter observed witness components appearing sporadically, hypothesizing it relates to disk availability and component placement challenges.

5. Performance Implications

ESA’s separation of performance and capacity legs optimizes write performance by handling writes first on mirrored performance legs before offloading to capacity legs.
This architecture should outperform the original vSAN RAID 5 implementation, which suffers write penalties.
Striping across multiple drives and hosts enhances read and write performance.
The lack of dedicated cache devices removes bottlenecks present in the original architecture.

Demonstrations and Analysis

Live examples of different failure tolerance policies (FTT=1, FTT=2) and RAID configurations (RAID 1, RAID 5, RAID 6) on a 5-host ESA cluster are shown.
Visualizations of components, subcomponents (striping), and their distribution across hosts are provided.
The presenter highlights how performance legs and capacity legs are structured and how they interact.
The absence or presence of witness components is demonstrated and discussed.
A new VM creation is used to illustrate when witness components may appear unexpectedly.

Guides and Tutorials Mentioned

Reference to earlier videos for foundational understanding:
- vSAN 101 (basic concepts)
- vSAN Striping video (explaining RAID 0 striping)
- “What’s new in ESA” video for adaptive RAID 5 details
An upcoming video is planned on setting up an ESA cluster.

Main Speaker

Steph (the presenter) — provides detailed explanations, live demos, and personal insights on VMware vSAN Express Storage Architecture components and behaviors.

Summary: This video serves as a technical guide and analysis of VMware vSAN Express Storage Architecture, focusing on how ESA changes component structure, eliminates traditional cache tiers, and modifies the role of witness components. It explains performance and capacity legs, RAID configurations, failure tolerance implications, and the occasional appearance of witness components, supported by live demonstrations on a vSAN Ready Node cluster.