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This article is part of our Essential Guide: VMware VSAN features and realities

How can I maximize ESXi cluster space in VMware VSAN?

An administrator wishing to implement the VSAN software-defined storage functionality in vSphere 5.5 can spare a drive for the cause.

How can I maximize the number of drives to use in VMware VSAN for an ESXi cluster?

VMware introduced Virtual VSAN (VSAN) in vSphere 5.5. VSAN allows administrators to take their existing ESXi servers and gather all the disks to pool them as a VM data store.

While there are certain requirements to meet before VSAN can be enabled, VMware feels this feature meets a technical and fiscal need in most VMware shops: It allows administrators to use their existing hardware and maximize the storage capacity without having to pay for the hardware and support from a shared storage vendor. VSAN also features resiliency through software, rather than a hardware RAID configuration.

Through the vSphere Web Client, administrators building an ESXi 5.5 cluster now have the option to enable a new software-defined storage option of VSAN. To use VSAN, the infrastructure must have a minimum of three ESXi 5.5 hosts -- each with at least 1 SSD drive and 1 hard disk drive (HDD) -- all managed by vCenter Server 5.5. The hosts must have a SAS or SATA adapter or a RAID controller in pass through mode. While the hosts can be networked with a 1 Gigabit Ethernet (GbE) connection, VMware recommends 10 GbE.

While in the beta phase, VMware limited the number of disks per host to seven -- six HDDs and one SSD -- but because many servers have space for eight disks, those limits were raised to seven HDDs and one SSD in the official release.

For administrators who want to maximize the number of disks per host for VSAN, using one drive solely for booting ESXi will seem a waste. There is a way around that.

"Most of my customers are booting off SD cards, because they want to save the drive slot in the hosts for VSAN capacity or SSD caching. It doesn't mean you couldn't take a physical drive and use that for a boot," said Peter Keilty, senior systems engineer at VMware, during his presentation on VSAN technical overview and best practices at the Boston VMUG User Conference on June 24.

"Chicken and the egg. ESX has to be up before VSAN can come up. You can't boot ESX off VSAN. You have to boot it off something, so you have to install ESX somewhere. It could be to a dedicated disk [or] a physical hard disk, but [you'll] want to save that drive slot so we're using SD cards for that. Most of the vendors out there support booting off the SD or USB," said Keilty.

This was last published in July 2014

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