VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
Virtual SAN storage requirements
This has already been covered in great detail when we looked at the VMware
Compatibility Guide. At this point, the importance of ensuring that the storage I/O
controller model chosen for a Virtual SAN is on the VMware Compatibility Guide
(VCG) should be clear, and that the driver and firmware versions of the storage I/O
controller should be at a supported level.
Another important factor is the class of flash device. This information is also found
on the VCG, and the higher the grade or class of flash device that is used, the better
the Virtual SAN performance.
However there are some points related to storage requirements that need to be
elaborated on.
Pass-thru mode versus RAID-0 mode
Virtual SAN prefers to be able to consume storage natively, and for that reason we
recommend devices be presented to ESXi from the storage controller in passthrough
mode. This means that the disks are visible to ESXi without the need of the
controller to place a volume (RAID 0) on them.
However not all of the storage controllers on the VCG allow devices to be presented
to the host in pass-through mode. In those cases, each individual disk device has to
be put into its own RAID 0 volume, and at the point, the ESXi host should be able to
discover it. This is not to be confused with the RAID 0 configuration implemented by
Virtual SAN stripe width via the policies. The RAID 0 referred to here is a
configuration place on the physical device by the controller, either through the BIOS
of the card, or via third party tools.
The reason for recommending pass-through over RAID 0 is that the replacement
process becomes much easier. New or replacement disks that can be plugged into a
host, and detected by ESXi, make disk management a lot simpler.
By examining the VCG output from earlier, when the HP storage controllers on the
VCG were listed, we can see that some require RAID 0 configurations, and others
support the pass-through mechanism (as listed in the Feature column):
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