The I/O controllers are as important to a VMware vSAN configuration as the selection of disk drives. vSAN supports SAS, SATA, and SCSI adapters in either pass-through or RAID 0 mode. vSAN supports multiple controllers per ESXi host.

  • Multiple controllers can improve performance and mitigate a controller or SSD failure to a smaller number of drives or vSAN disk groups.

  • With a single controller, all disks are controlled by one device. A controller failure impacts all storage, including the boot media (if configured).

Controller queue depth is possibly the most important aspect for performance. All I/O controllers in the VMware vSAN  Hardware Compatibility Guide have a minimum queue depth of 256. Consider normal day-to-day operations and increase of I/O due to Virtual Machine deployment operations or re-sync I/O activity as a result of automatic or manual fault remediation.

About SAS Expanders

SAS expanders are a storage technology that lets you maximize the storage capability of your SAS controller card. Like switches of an Ethernet network, SAS expanders enable you to connect a larger number of devices, that is, more SAS/SATA devices to a single SAS controller. Many SAS controllers support up to 128 or more hard drives.

Caution:

VMware has not extensively tested SAS expanders, as a result performance and operational predictability are relatively unknown at this point. For this reason, you should avoid configurations with SAS expanders.