In a VMware ESXi infrastructure, shared storage is a no-brainer.
Once a physical server goes down, the virtual machine (VM) files that reside on that server become unavailable as well. With shared storage, however, another ESXi host can access and start the VMs that were running on a failed server.
But you don't need an expensive storage area network (SAN) to benefit from shared storage. There are two, free ways to that create a shared-storage infrastructure for VMware ESXi: FreeNAS and Openfiler.
Configuring shared storage in FreeNAS is an easy, two-step procedure. First, define a volume on the FreeNAS server, which is the disk that stores the images. Next, indicate how you want to access the volumes. FreeNAS is based on network file-sharing protocols, and you can choose from Network File System (NFS), Windows' Common Internet File System or the Apple Filing Protocol. Of these choices, VMware ESXi supports only the NFS storage protocol.
Because FreeNAS is based on a file-sharing protocol, there is some overhead when writing packets to the shared storage. If you're predicting a high amount of disk I/O, this protocol may slow down the system too much. In that case, a SAN may be better.
If you've ever worked with SAN products from NetApp Inc., you'll notice similarities to the Openfiler interface, which has a comparable look and feel. Openfiler offers real SAN functionality, which means you'll receive performance benefits from giving remote machines access to block devices and not to file systems. In fact, OpenFiler can even create an iSCSI SAN.
First, download the free Openfiler software and install it to a dedicated machine. If you accept the defaults, the installation is easy. These settings make all your disk space available to Openfiler.
For more granular storage--provisioning options, such as the ability to configure shared storage for client nodes, use the Openfiler Web interface. From here, you can easily set up the shared storage as either a SAN (shared devices) or NAS (shared file systems). The included iSCSI target is fast, which makes Openfiler a favorite choice for a free shared-storage arrangement.
FreeNAS offers a Unix-based configuration for access to files, and Openfiler offers a Linux-based approach to access block devices. From a performance standpoint, the latter solution is preferred. But both tools install easily and allow multiple ESXi hosts to access virtual machines in a shared-storage arrangement. So from that perspective, you can use either product.
This was first published in May 2011