ESXi SD-Card/USB boot devices unsupported in 7.0u3

Published by Christian Mohn · Read in about 3 min (605 words)

In the ongoing saga of SD-Card/USB-boot device support in ESXi, VMware has just published a new KB article named “Persistent storage warnings when booting ESXi from SD-Card/USB devices. (85615)” outlining that from 7.0u3 (at the time of writing, not released yet) onward support for such boot devices is deprecated.


As of 03. September 2021 the Persistent storage warnings when booting ESXi from SD-Card/USB devices. (85615) KB article has been removed from for unknown reasons. Hopefully it will be back soon.


Update 16. September 2021: A new KB article has been published: Removal of SD card/USB as a standalone boot device option (85685). This article outlines that from the next major version, after 7.x, using standalone SD card/USB will be unsupported, with the following notice: “VMware strongly advises that you move away completely from using SD card/USB as a boot device option on any future server hardware.

ESXi requires local persistent storage for operating system use, to store system state, configuration, logs, and live data. A system with only a SD-Card/USB boot device is operating in an unsupported state with the potential for premature corruption.

They also list the workarounds for this as either install to a non SD/USB device, or to add a persistent storage device.

Additional information can also be found in Boot device guidance for low endurance media(vSphere and vSAN) (82515), which somewhat contradictory states that upgrades will still be supported in 7.x.

For all upgrades ESXi 7.0 onwards, we continue to support existing boot devices.

I have a suspicion that is 7.x specific, and that will change in a future version, and that ESXi might not even install on SD-Cards and USB thumb drives at some point.

While I completely support and understand why VMware is doing this, and I would never recommend anyone running their production vSphere environments on hosts booting from SD-Card/USB boot devices, this might be an issue for homelab setups, especially those running vSAN. While small form factor nodes, like the Intel NUC, is inherently unsupported from VMware anyway, the new requirement of having a location to place the ESXi OS Data might be a problem. Many small form factor setups only allow two internal devices, typically one M.2 and one SATA3 device, and since vSAN requires a minimum of one cache drive and one capacity drive per disk group, this might be a problem for many small setups.

One alternative is using booting the hosts from a resilient external USB drive (HDD/SSD/NVMe) in an enclosure, since using a USB device isn’t the real problem, but rather that the resiliency of the NAND chips on a SD-card or USB thumb drive isn’t suited for the storage scheme and layout introduced in ESXi 7.0.

Another possibility is using USB storage for vSAN, or even using something like an rPI as an iSCSI target, either way you’ll need something outside of the vSAN cluster hosts themselves to ensure ESXi keeps running.

Just like with everything else, plan accordingly.

I do applaud VMware for being transparent about this. Publishing the new KB article before ESXi 7.0u3 is released is also good. Seems that part was premature, since the KB has since been pulled from the public.

I think removing support for a boot option in a update release and not a major release is a bit strange. Anyone who is still running production vSphere hosts on SD-Card/USB thumb drives needs to take action as soon as possible to ensure support going forward. I am sure further guidance will also be given before the 7.0u3 update is released as well, especially now that the original KB has been pulled.

Post last updated on January 2, 2024: Add author

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