6.5.1

Table Of Contents
Troubleshooting Flash Devices
vSphere uses flash drives for such storage features as vSAN, host swap cache, and Flash Read Cache.
The troubleshooting topics can help you avoid potential problems and provide solutions for issues that
you might encounter when configuring flash drives.
Formatted Flash Devices Might Become Unavailable
A local flash device becomes unavailable for virtual flash resource or Virtual SAN configuration when it is
formatted with VMFS or any other file system.
Problem
When you attempt to configure either vSAN or virtual flash resource, a local flash disk does not appear on
the list of disks to be used.
Cause
This problem might occur when flash disk intended for use with either feature has been already formatted
with VMFS. Virtual flash and vSAN cannot share the flash disk with VMFS or any other file system.
Also, because virtual flash and vSAN are mutually exclusive consumers of flash disks, both features
cannot share a flash disk. If the flash disk is already claimed by one feature, for example vSAN, you
cannot use it for another, such as virtual flash, unless you release the disk.
Solution
Use only unformatted flash disks for virtual flash resource and vSAN configuration.
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Avoid formatting the flash disks with VMFS during ESXi installation or Auto Deploy.
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If the flash disk is already formatted with VMFS, remove the VMFS datastore. For information, see
the vSphere Storage documentation.
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To use the flash disk as a virtual flash resource, do not claim this disk for vSAN. If the disk is claimed
by vSAN, remove the disk from vSAN. The flash disk is released from vSAN and becomes available
on the list of disks to use with virtual flash. For information about removing disks from vSAN, see the
Administering VMware vSAN documentation.
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If you intend to use the flash disk with vSAN, do not use the disk for a virtual flash resource. If the
flash disk is used as the virtual flash resource, remove the virtual flash configuration. The disk
becomes available for vSAN. See the vSphere Storage documentation.
Another reason that makes flash disk unavailable is when ESXi cannot detect the disk. See Local Flash
Disks Are Undetectable.
Keeping Flash Disks VMFS-Free
If you use the auto-partitioning boot option when installing or auto-deploying ESXi, the auto-partitioning
option creates a VMFS datastore on your host's local storage. In certain cases, you need to keep your
local storage flash disks unformatted.
vSphere Troubleshooting
VMware, Inc. 74