Shooting yourself in the foot is bad (Where are my swap files?)

vSphere by default stores vswap files (the files used when your host runs out of physical memory to allocate) with the local machines. However, you can choose (on a per VM or per-host basis) to direct all swap files to one location.

VMware admins redirect swap files for many reasons – lower cost of local disk space, array-based reasons (snapshots, replication) etc – but not many of them know that the setting might change back to “keep with the virtual machine” automatically!

Here is an ESXi 5 host in a cluster. Since the arrays available to me are virtual/demo ones with very limited space I set the host to keep the swap files on the ESXi server’s “local” disk.

Ok, no problem! When I fire up or vMotion a VM to this host (assuming the vMotioned machine’s swap file isn’t on shared storage!) the swap file gets created on the local disk.

However, I need to be careful with the maintenance I do to the host – if I remove it from the cluster (regardless of “swap file location” settings on the cluster) the host is reset to the default!

Now if I power cycle my VMs they won’t start up at all, until I either increase their reservations or change the swap file settings on either the VMs or host.

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