VMware ESXi – SD Card Vs. HDD

This article compares VMware ESXi on an SD card Vs. ESXi on an HDD. Deciding whether to install VMware ESXi onto an SD card or HDD is an important decision and basically comes down to the following:

  • The hardware differences of SD card’s Vs. HDD
  • The software differences of ESXi on an SD card Vs. HDD

Hardware Differences Of ESXi On SD Cards Vs. HDD

These are the main hardware differences between installing ESXi on SD cards rather than HDDs:

  • SD cards have a limited number of writes before they become useless (Though this point is mute due to the software differences of SD Vs. HDD, but I thought I’d mention it because it’s the obvious difference that people talk about)
  • SD cards do not have S.M.A.R.T capability, which means that there is no reporting when they start to develop faults
  • The fact that SD cards don’t have S.M.A.R.T reporting is compounded by the way that they die when they fail; You will get no alert that they are failing, they will just get slower then suddenly stop working one day
  • SD cards are cheaper than HDD’s (Although more expensive if using VMware’s best practice and don’t have a syslog server [Check the bullet points under the software differences of ESXi on SD cards Vs. HDDs])

I don’t want to talk about whether SD cards or HDD’s are faster, because technology changes… though at the time of writing, HDD’s are faster (because we have SDDs).

Software Differences Of ESXi On SD Cards Vs. HDD

This is an interesting point: Installing ESXi onto an SD card automatically installs ESXi Embedded, while installing ESXi onto an HDD >5GB in size installs ESXi Installable.

This article doesn’t discuss an in depth comparisson of ESXi Embedded Vs. Installable, but it’s worth pointing out these key differences that effect considerations when comparing SD card and HDD installations:

  • ESXi Embedded (Automatically installed on SD cards) writes to disk less… Making hardware issues of SD cards only having a limited number of writes insignificant
  • When using ESXi Embedded, as logs are not recorded on the SD card by default, it is recommended by VMware to install an additional drive (HDD) to store logs for troubleshooting ESXi host issues. Another way to deal with this is to send the logs to a syslog server if you have one

An Alternative To SD Cards And HDDs

So by now you’re probably thinking either to use HDDs because they’re better or your thinking to use SD cards if you have a syslog server, because it’s cheaper… But I would like to give you an alternative option to consider: Autodeployed / PXE booted ESXi.

Autodeployed / PXE booted ESXi boots straight from the network and does not require an SD card or HDD of any kind, because it runs entirely in RAM.

Discussion of this is kind of out of the scope of this article, I really wanted to just stick to comparing SD Cards Vs. HDDs, so you might want to do some more research 😉

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