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Quick Tip - How to monitor when ESXi filesystem and partitions are filling up?

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Here is another tidbit on how you can leverage the power of vSphere Events, which now includes over 2K+ as of vSphere 8.0 Update 1 to help monitor when an ESXi filesystem and/or partition is low on disk space.

With vSphere 6.7 or later, we have two events that you can use to help alert when either an ESXi ramdisk (e.g. /var) or VFAT partition (e.g. bootbanks) has filled up.

  • Ramdisk: esx.problem.visorfs.ramdisk.full
  • VFAT: esx.problem.vfat.filesystem.full.other

When either of these occur, you can easily find them under the Monitor->Events section for an ESXi host as shown in the screenshot below.

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Is the vCenter Server Unique ID still important today?

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When I was a customer back in the day, one of my operational checklist items for deploying a vCenter Server was to configure the vCenter Server ID and ensure that it was unique from other vCenter Servers within my environment.


The vCenter Server ID is a value between 0-63 that is randomly generated by default, but it can updated by a user after the vCenter Server has been deployed.

Why should you care about the vCenter Server ID? vCenter Server uses this ID to generate Virtual Machine MAC Addresses and if two vCenter Servers have the same ID, it can potentially generate duplicate VM MAC Addresses as explained in this VMware KB 1024025.

With this background in mind, is having a unique vCenter Server ID still relavent and applicable today in 2022?

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Does vCenter Server recycle VM MAC Addresses after Cross vCenter vMotion?

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I recently received a question from a customer who was concerned that after a VM has been migrated from one vCenter Server to another using Cross vCenter vMotion, that the original source VM MAC Address could potentially be recycled and re-used at a later point. Back in 2015, I actually wrote about this very topic and the concerns around VM MAC Address duplication after a Cross vCenter vMotion, which I highly encourage folks to check out if you have not seen this article already.

While re-reading the article, I realized that the article had primarily focused on vCenter Servers that were in Linked Mode or under the same vSphere Single Sign-On (SSO) domain and although I did mention the Cross vCenter vMotion across across different vSphere SSO domains scenario, it looks like the details were a tad bit light.

To quickly summarize, when a VM is migrated from a source vCenter Server to the designation vCenter Server, the VM's MAC Address is added to a MAC Address "block list" on the source vCenter Server. This ensures that the VM MAC Address will not be reallocated by the source vCenter Server which would cause a network conflict. This has been the default behavior since vSphere 6.0 and no additional configuration change is required by customers.

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