Should I replace the SD/USB disks or still can keep them?

I think many of us read about the new features on the release of vSphere 7.0 Update3 and like many people that asked me about, you may be concerned about keeping the procedure of ESXi installation on SD Cards or USB Drives. Using these types of disks as the ESXi boot device is common, just because they have a lower cost in comparison to other types of storage. 

VMware has been changed the ESXi BootBank architecture and created the ESX-OSData partition, and there is a major difference between the current and older versions. I mentioned some of them in this Post: ESXi BootBank partitions. I suggest reading this post if you decided to change your hypervisor setup plan. However, Bob Plankers described the limitations and restrictions of NAND Flash memories in vSphere7 Up3 What's new truly perfect.

In addition, you should know the ESXi 7.0 is required at least 32GB of disk space to store ESX-OSData. So, keep in mind boot devices especially lower capacity devices (less than 32GB) aren’t suitable anymore in new version.

You need enough space for ESX-OSData (consists of Dump and Log files) it’s still recommended to change their location to local HDD/SSD media if you want to keep the existing (SD/USB) boot device structure. So according to the recently ESXi structure variations, you need to choose one of the following installation procedures:

 1. Using local HDD/SSD disks for both of ESX-OSData and Boot. The oldest method of installation and consequently still supported by VMware, so you can keep going through this way.

2. Flash Local HDD/SSD disks for keeping ESX-OSData and NAND Flash used as the System Boot and BootBank partitions. VMware calls this structure Legacy, while still is supported but it's better to change your Boot devices ASAP.    

3. Using only SD/USB disks is Deprecated in vSphere 7.0 Update 3 because of their poor performance and lower capacity than HDD/SSD disks. So it's strongly recommended to reconsider the setup plan for new ESXi hosts.

You can read the vSphere Team's blog Post about the Boot Media Considerations.

For more information, if you need to know how to change the log files (/scratch/log) directory to another persistent storage, you can achieve this goal through modifying this advanced system parameter: Syslog.global.LogDir
Also, to change Coredump physical path to another partition for collecting dump files, review this post.