vSAN ESA with VMware Cloud on AWS: Technical Deep Dive


With version 1.24 of VMware Cloud on AWS SDDC vSAN Express Storage Architecture (ESA) has been released. It may not be initially available to all customers or in all Regions or Availability Zones and customers are encouraged to engage with the VMware team to understand its availability and enable the feature.

When deploying a new SDDC or a new cluster with the i4i host type you can now choose between the “original” (OSA) or “express” (ESA) vSAN storage architecture. Let us look at the capabilities, supported use cases, deployment scenarios, and benefits of vSAN ESA on VMware Cloud on AWS.

vSAN Express Storage Architecture Overview

vSAN ESA was introduced with vSphere 8 and enhanced in the vSAN 8 U1 and U2 updates. It is designed to utilize the full capabilities of modern hardware and delivers high performance and scalability

vSAN ESA leverages single-tier storage architecture utilizing high-performance NVMe devices opposite to two-tier vSAN Original Storage architecture (OSA) where cache and capacity tiers are separate. Using a single-tier architecture increases the overall capacity available and narrows the impact of drive failures.

With other improvements including a new log-structured file system, improved compression technique, redesigned encryption process and native snapshots vSAN ESA provides lower TCO, faster, more reliable storage architecture with improved capacity and performance without compromise. You can find a comprehensive review of new Express Storage Architecture features and benefits on the vSAN Express Storage Architecture (ESA) Techzone page.

vSAN ESA Overview

vSAN ESA Implementation Details on VMware Cloud on AWS

Prerequisites and Limitations

Clusters with new vSAN architecture are supported with i4i.metal host type only.

  • vSAN ESA makes its first appearance with VMware Cloud on AWS 1.24. With this release, we support the following use cases:
  • New SDDC deployment (both the primary and secondary clusters),

Combining OSA and ESA deployment in the same SDDC,

We are looking to make vSAN ESA available for existing SDDC in the future.

vSAN OSA to ESA cluster conversion or vSAN in-place upgrade capabilities are on the roadmap and not available now.

Supported Scenarios

The list below represents a list of supported vSAN ESA deployment scenarios for 1.24 SDDCs:

  • Greenfield SDDC, Primary vSAN ESA Cluster 3 host onwards
  • Multi-cluster deployment for existing 1.24 SDDCs:
    • 1st cluster OSA + 2nd Cluster ESA
    • 1st Cluster ESA + 2nd Cluster OSA
    • 1st & 2nd Cluster both ESA

vSAN ESA SDDC Deployment

vSAN ESA Benefits with VMware Cloud on AWS

With vSAN Express Storage Architecture on i4i hosts VMware Cloud on AWS customers are getting instant capacity benefits and storage performance increase compared to vSAN Original Storage Architecture.


vSAN ESA removes the need for dedicated cache devices making the capacity of all NVMe drives usable by the vSAN datastore.


Let us illustrate the capacity gains by example: when deploying a vSAN ESA cluster with i4i nodes customers would get 27.28 TiB (8 disks*3.41 TiB ) raw capacity, compared to 20.46 TiB (6 disks* 3.41 TiB) using traditional vSAN OSA with 2 disk groups effectively claiming 2 disks for cache on each host i4i giving impressive 33% increase for raw capacity available.

The table below contains raw capacity calculations for the vSAN ESA cluster supported in VMware Cloud on AWS SDDCs.

ESA / i4i vCenter Reported Disk Sizes
3.41 (TiB) NVMe Disk Size
27.28 (TiB) 8 disk * 3.41 - RAW (TiB)
81.85 3 Node RAW
109.13 4 Node RAW
136.42 5 Node RAW
163.70 6 Node RAW
190.98 7 Node RAW
218.27 8 Node RAW
245.55 9 Node RAW
272.83 10 Node RAW
300.12 11 Node RAW
327.40 12 Node RAW
354.68 13 Node RAW
381.97 14 Node RAW
409.25 15 Node RAW
436.53 16 Node RAW

vSAN RAID-5 policy is available for clusters as small as 3 nodes and RAID 6 is enabled starting from 6 nodes during deployment of vSAN ESA cluster in SDDC bringing additional capacity gains specifically for small cluster deployments.


With the new Express Storage Architecture compression process is now executed on the ESXi host where the virtual machine is running minimizing CPU and storage writes amplification required and decreasing network traffic.

Putting compression “up the stack” allowed it to move its configuration to VM or even virtual disk level differing from vSAN OSA where it was a datastore level setting.

The improved compression algorithm can reduce the 4KB block size to as little as an 8:1 ratio which is 4 times better compared to vSAN OSA which could theoretically achieve a 2:1 compression ratio.

Compression is enabled by default and recommended for most of the workloads but can be disabled using the “No Compression” policy (i.e. use cases where applications are performing their own compression) saving CPU cycles.

Changing the compression policy on existing objects will affect only subsequent writes and will not change the compression state of existing data retroactively. This removes performance impact compared to vSAN OSA where changing compression configuration forced re-writing all data to the vSAN datastore.


vSAN ESA is designed to deliver higher performance for both read and write workloads. This is due to a number of factors, including the use of a log-structured file system and reduced write amplification.

Log-structured file system (LFS) implementation in vSAN ESA allows very fast ingesting of incoming small-writes and writing them to durable log which is tied to specific vSAN object and mirrored as a component across hosts depending on the FTT policy for the object. This is called the “performance leg” and allows to provide write acknowledgment to the guest virtual machine with minimal latency.

When the object’s durable log becomes full LFS writes data to the “capacity leg” which is another branch of vSAN object data. Write is performed in full stripe and aligns with the assigned policy for the object.

Such an approach reduces CPU and I/O amplification required and eliminates traditional RAID-5/6 trade-off for capacity over performance. You can find a detailed overview of the vSAN log-structured file system in the article: RAID-5/6 with the Performance of RAID-1 using the vSAN Express Storage Architecture.

Native snapshots capability delivered with vSAN ESA Architecture allows to minimize performance degradation regardless of the number of snapshots taken. The new approach is using a highly efficient lookup table instead of a traditional chain of base and delta disks. vSAN ESA LFS performs incoming writes with the appropriate metadata pointers providing the intelligence behind which data belongs to which snapshot. This speeds up snapshot operations which are one of the most intensive yet frequent activities and makes it much more efficient compared to traditional vSAN OSA architecture. You can find more details in the article: Scalable, High-Performance Native Snapshots in the vSAN Express Storage Architecture.

Data at rest encryption is enabled by default on each VMware Cloud on AWS SDDC cluster and can't be turned off. For vSAN ESA this data service similar to compression is performed on an ESXi host level before writing data to disks thus making less impact on the performance when compared to the OSA. More details on encryption improvements can be found in the article: Cluster Level Encryption with the vSAN Express Storage Architecture.

Less Impact Of a Disk Failure

Using a single-tier architecture increases the overall capacity available and narrows the impact of drive failures. Eliminating the vSAN OSA disk group concept where a failing cache drive led to the failure of the whole group narrows the failure domain in vSAN ESA to a discrete disk reducing the amount of data affected in case of the error.

vSAN ESA Failure Impact


vSAN Express Storage Architecture is one of the key features introduced with the new 1.24 release of VMware Cloud on AWS.

Supported on primary and secondary clusters running on i4i hosts customers could gain immediate benefits from modern vSAN architecture getting more capacity and performance and lowering TCO.

With better compression, native snapshots and encryption which requires less overhead, vSAN ESA is a no-brainer choice for customers running workloads on VMware Cloud on AWS.

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