Comparing Shared Storage Approaches for VMware vCenter Cluster

The common technique for increasing redundancy, high availability, and load efficiency for a vSphere environment is to arrange ESXi hosts into vCenter cluster. One of the most important requirements for clusters is creating a shared storage. There are several ways to do this:
  • SAS interfaces on storage servers and an ESXi host
  • Fibre Channel
  • iSCSI
  • Virtual SAN (vSAN)
Let’s take a look at each of them and then compare the approaches.

SAS Interface

SAS Interface is an approach which requires hardware SAS interfaces on both server and client sides. The indicated technology provides speeds of up to 12 Gbit/s (which is true for SAS-3, and we’re expecting SAS-4 in 2017 with up to 22.5 Gbit/s), but it has several limitations. First of all, SAS infrastructure is not scalable because of the finite number of SAS ports on the storage server. However, if you need more storage, you must replace disks with larger ones or install an additional storage server. Second, a storage server and disks must be mounted in the same rack because of the cable length. Thus, this approach works well for small-to-medium environments with high data transfer speed demands.

Fibre Channel Technology

The Fibre Channel Technology requires additional hardware as well: an FC-controller on a storage server and host-based adapters (HBAs) for each ESXi host in the vCenter cluster. In addition, you will need FC-switches if the number of ESXi hosts is greater than the number of FC ports in the storage. Such layout is common for large server infrastructures.

The biggest advantage of Fibre Channel is speed. FC ‘Gen 6’ networks provide 12,800 MB/s throughoutput per direction. Given that, you can build a fully-functional high-speed network. But the price of equipment is really sky-high. Such infrastructure suits large banks and corporations, where data transfer speed and security are the highest priorities.

iSCSI

Unlike SAS or FC, iSCSI technology does not require any specific hardware. It works within existing Ethernet network infrastructure and uses software-emulated iSCSI adapters. This makes the technology easier to scale than the previous two since you don’t need any additional equipment.

On another hand, iSCSI requires a dedicated server with a specific OS and software configuration to make it work.

iSCSI might be a solution for small environments with small IT budgets, as it doesn’t require additional equipment.

vSAN

As of vSphere v5.5 launch, VMware promotes its own approach for creating shared VMFS storages. They recommend using local server resources and existing Gigabit Ethernet networking without additional storage server hardware.

This option looks attractive since it does not need any specific hardware and can be configured via a GUI. Moreover, it does not rely on the physical location of your hosts and storage disks.

The drawback is that vSAN requires an additional license, which can be pricey depending on the number of hosts.

vSAN is a good choice for the infrastructure of any size and is especially handy if you are not able to install a dedicated storage server, but it may become a costly solution for larger datacenters.

Shared Storage Approach Comparison for VMware vCenter Cluster

To make the long story short, here’s a brief comparison table of these approaches.

Approach Additional Hardware Additional Software Dedicated Server Management Complexity
SAS SAS interfaces Yes Yes Medium
Fiber Channel FC-controller, HBA, FC-switchess Yes Yes Dedicated admin needed
iSCSI No Yes Yes Specific server configuration needed
vSAN No No No Configured via vSphere Web-Client

Thoughts

Before starting a physical-to-virtual migration project it’s better to conduct a feasibility research to determine the IOPs number for virtualized servers. Based on its results, you will decide which storage arrangement approach works best for you.

In the next post, we’ll take a closer look at the vSAN configuration and its pitfalls.

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