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Stilez
Asked: 2017-04-30 07:00:35 +0800 CST

ESXi - distinction between Host Cache, VM Swap File, System Swap, vFlash?

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In ESXi 5.5, the host config has a number of similar sounding settings related to swapfiles and caches of various types.

I understand the principles of write-back/write-through disk cache and swapping VM swap files to the host instead of their remote VMDKs, and I'm reading the docs, but it's still pretty confusing which of these is which, and how they inter-relate within ESXi.

For information, my system has a single standalone host with 96GB RAM and three datastores - a local boot store, an iSCSI main store, and a 250 GB NVMe SSD for swap/cache use.

A clear explanation of the differences and how they work together would be really useful right now :)

vmware-esxi

2 Answers

  1. Host cache: deprecated.

    Use Flash Read Cache instead. You can reserve a Flash Read Cache for any individual virtual disk. The Flash Read Cache is created only when a virtual machine is powered on, and it is discarded when a virtual machine is suspended or powered off. Obviously, this cache can only operate in Write-Through mode.

    VM Swap & Host Swap

    Read this article for better understanding: http://pawellakomski.pl/blog/types-of-swapping-on-esx-hosts/

    Web Archive https://web.archive.org/web/20161116081952/https://pawellakomski.pl/blog/types-of-swapping-on-esx-hosts/

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  2. I wouldn't touch any of the Swap settings or modify from default. Ideally you wouldn't be swapping because you planned for enough RAM to handle your VM workload, right?

    vFlash is just a read cache that can lower latency for network-based storage or frequently-read data. It's set per-VMDK (not just per-VM).

    If you want the best performance for your single-host setup, use internal disks.

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