Example Architectural Decision – Number of paths per LUN for VMFS datastores

Problem Statement

In a vSphere environment hosting a large number of VMs,  Virtual machines I/O requirements range from small <100 IOPS to large business critical applications with tens of thousands of IOPS, the ESXi hosts have been configured with 4 x 8Gb FC HBAs.

What is the most suitable number of paths per LUN when using 4 x 8GB FC connections per Host, and how will they be presented in a highly available manner with two (2) SAN Fabrics connected to an Active/Active Enterprise Disk array?


1. All LUNs are available on all FC Interfaces
2. The storage be highly available
3. The environment should be able to continue running production workloads in the unlikely event of a dual port HBA, or single Fabric failure.
4. The environment maintain a consistent level of performance


1. The Storage area network has two (2) fabrics each of which is highly available
2. The disk system is presented to both SAN fabrics
3. The number of VMs per host is >100
4. vSphere 4.0 or later
5. Storage array is Active/Active
6. ESXi hosts are large and are designed to drive significant I/O
7. VAAI is supported and enabled


1. Maximum paths supported per ESXi host is 1024
2. Maximum number of datastores per ESXi host is 256


1. Ensure optimal performance redundancy
2. Maximum the total capacity able to be presented to a cluster

Architectural Decision

Use a standard of 8 paths per LUN

Each LUN will be presented to each HBA via both Controller A and Controller B resulting in two paths per LUN per HBA.

With a total of 4 FC connections across two (2) physical dual port HBAs in a HA configuration with one (1) connection per HBA per Fabric, this equates to a total of 8 paths per LUN to the ESXi host (4 paths per Fabric)


1. This equates to 4 paths (1 per HBA interface per LUN) per Fabric
2. The use of VMware NMP with “Round Robin” will be used and having all LUNs presented via both fabrics and all HBAs will provide the maximum reducing in latency and the most consistent performance overall
3. 8 paths per LUN ensures up to 128 LUNs can be presented within the 1024 paths per ESXi host limit which will support sufficient capacity for the cluster
4. The solution is highly available as it uses two fabrics and both controllers are Active
5. In the event of a Fabric failure, the remaining Fabric serving 2 x 8Gb connections will provide connectivity to both Controller A and B, with a total of 4 paths
6. Ensures the cluster can have enough LUNs to balance workloads across which will assist keeping latency at a minimum


1. Have less paths per LUN which enabled the use of more LUNs
2. Have more paths per LUN and have less LUNs


1. LUN sizes will need to be sizes to ensure a maximum of 128 LUNs are sufficient from a capacity perspective to cater for the desired number of virtual machines


One thought on “Example Architectural Decision – Number of paths per LUN for VMFS datastores

  1. Hi Josh – Great post, please let me ask you. Would you have a diagram of this solution? I want to make sure I am reading this right. I am thinking you are talking about a single ESXi host with 2x Dual-Port HBAs. This host is connected to two SAN switches and each switch connected to two Storage Ports (active/active). Something like this;
    ESX-HBA#1 Port#1 – Switch#1 – Controller#1- StoragePort#1
    ESX-HBA#1 Port#2 – Switch#2 – Controller#1 -StoragePort#2
    ESX-HBA#2 Port#1 – Switch#1 – Controller#2 -StoragePort#1
    ESX-HBA#2 Port#2 – Switch#2 – Controller#2 -StoragePort#2

    Does that makes sense, am I reading this correctly?

    Thank you