In this blog post MicroSD card RAID 1 as VMware ESXi boot device I wrote about the HP dual-microSD card module. This small piece of hardware provides data redundancy through a mirrored RAID 1 configuration and you can use it as an ESXi boot device.
Unfortunately, there seems to be a lot of problems with version 001 and 002 of the product. A lot of readers complained in the comments about issues, and I experienced some unexpected problems, too:
“Configuration Issues | Lost connectivity to the device […] backing the boot filesystem /vmfs/devices/disks/mpx … As a result, host configuration changes will not be saved to persistent storage.”
It seems, that in some situations the host experiences an all path down scenario and lost the connectivity to the SD card.
The good news: as ESXi runs in memory once it is started, there is no problem with production and the host keeps on running. If you want to get rid of the issue you just have to shut down the host and start it again. But this can only be a workaround.
If you experience the issue, too I recommend you to open a case with HP. There seems to be a problem with version 001 and 002 of the device. Version 003 should be working without problems.
The latest version has another design, so they are easy to distinguish. The version is imprinted on the stick, just search for the product number: