VMware has not been very clear on the communication about, the support for booting ESXi on USB/SD-Card from the release of ESXi 7.0.
In the original documentation, the requirement for installing/upgrading ESXi 7.0 it says that USB/SD-Card in support for boot media:
“ESXi 7.0 requires a boot disk of at least 32 GB of persistent storage such as HDD, SSD, or NVMe. Use USB, SD and non-USB flash media devices only for ESXi boot bank partitions. A boot device must not be shared between ESXi hosts.”From documentation.
“For best performance of an ESXi 7.0 installation, use a persistent storage device that is a minimum of 32 GB for boot devices. Upgrading to ESXi 7.0 requires a boot device that is a minimum of 4 GB. When booting from a local disk, SAN or iSCSI LUN, at least a 32 GB disk is required to allow for the creation of system storage volumes, which include a boot partition, boot banks, and a VMFS-L based ESX-OSData volume. The ESX-OSData volume takes on the role of the legacy /scratch partition, locker partition for VMware Tools, and core dump destination.”From documentation.
This says that USB/SD-Card it fully supported, but there was a note that it was recommended to not to use USB/SD-Card for boot media, nothing about deprecated this for the ESX-OSData volume, in future version.
After ESXi 7.0 Update 2 came out, a lot of customer had problem with there hosts, since the USB Driver that is also used for SD-Card had a bug in the queue length/size. this got fixed in version 7.0 Update 2c.
After this VMware first published a KB that said that version 7.0 Update 2 was the last version to support boot from USB/SD-Card and also have th ESX-OSData disk on this. So the solution was to and another media like SSD/HDD/NVMe/M.2/.. and move the ESX-OSData to this. This KB got retracted after 1 or 2 days.
Afterward the publish a new KB with information about this again, this is a little more clear, that after 7.x ESX-OSData is not supported on USB/SD-Card, so you need another device for this: SSD/HDD/NVMe/M.2/.
But in a new Blog from VMware It says that this will not be supported in the next major version after 7.0 Update 3.
“The use of standalone SD cards or USB Drives (No additional device available for ESX-OSData partition) as boot media to store the ESX-OSData partition is being deprecated in vSphere 7 Update 3 and will not be supported in future major releases.”From this VMware Blog
This does not make anything more clear, if the next version is 7.1 og 7.5 will it be supported, or not. but with version 8.x it will not be supported, so the question is will the next release be a 7.x og 8.0.
My conclusion must be, do not use USB/SD-Card as boot media, it does not make sense to have both at USB/SD-Card and another device in the servers for the ESX-OSData, just use a supported device for both.