I have two VMware vSphere home labs with relatively old hardware (10+ years old). Even I have upgraded the old hardware to use local SATA SSD disks or even NVMe disks the old systems does not support boot from NVMe. That's the reason I still boot my homelab ESXi hosts from USB flash disks, even it is highly recommended to not use USB flash disks or SD cards as boot media for ESXi 7 and later. The reason for this recommendation is to keep boot medium in healthy state even ESXi 7 and later writes more frequently to boot media then earlier ESXi versions. If you want to know more details about reasons for this recommendation, please read my older post vSphere 7 - ESXi boot media partition layout changes.
During the ESXi installation you can choose USB disk as boot medium and local NVMe disk as a disk for ESX OSDATA partition, which will be used to write ESXi system data like config backups, logs (ESX, vSAN, NSX), vSAN traces, core dumps, VM tools (directory /productLocker), and other ephemeral or persistent system files.
How it looks like and how you can identify ESX OSDATA partition on local disks?
vCenter / vSphere Client
Interestingly enough, if you check disk partition layout form vCenter, you will see this 128 GB partition identified as "Legacy MBR". See the screenshot below.
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| ESX OSDATA Partition details in vSphere Client - Legacy MBR (128 GB) |
This is, IMHO, little bit misleading.
ESXi host Web Management
You can connect directly into particular ESXi host and check the partition diagram in ESXi host web management. See the screenshot below.
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| ESXi OSDATA partition details about NVMe disk - VMFSL (128 GB) |
There is no information about "Legacy MBR" partition but it is identified as "VMFSL" partition. So again, there is not explicit information about ESXi OSDATA partition but it is identified as VMFSL file system. What is VMFSL? VMFSL in ESXi stands for VMware File System Logical — it's not an officially documented term in VMware's main literature, but it refers to an internal filesystem layer used by ESXi for managing system partitions and services that aren’t exposed like traditional datastores (VMFS or NFS).
It is, IMHO better information than vSphere Client provides via vCenter.
ESXi Shell
We can also list partition tables in ESXi Shell.
[root@esx22:~] partedUtil getptbl /vmfs/devices/disks/eui.0000000001000000e4d25cc9a0325001
gpt
62260 255 63 1000215216
7 2048 268435455 4EB2EA3978554790A79EFAE495E21F8D vmfsl 0
8 268435456 1000212480 AA31E02A400F11DB9590000C2911D1B8 vmfs 0
It is also listed as VMFSL partition, but we can also see partition GUID.
The GUID (Globally Unique Identifier) that identifies the partition type. This GUID is unique to the partition and corresponds to a specific partition format (e.g., VMFS6, OSDATA, etc.).
And that's it. Now you know all details about ESX OSDATA partition and how to identify it.
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