In the partition layout, we saw that a scratch partition is created during the ESXi installation procedure. But what is the scratch partition, exactly? The scratch partition is a 4 GB VFAT partition used for storing temporary data, including logs, diagnostic information, and system swap. Although the scratch partition is not required, VMware recommends that ESXi has a persistent scratch location available. If the scratch partition is not configured, /scratch is located on the ramdisk linked to /tmp/scratch.

Leaving the scratch partition on the ramdisk will affect performance and memory optimization; therefore, it is recommended to create the partition in a suitable destination.

If ESXi is installed on a destination such as an SD card or a USB stick, the scratch partition is not created. As result, an annoying warning message will be displayed in the UI that advises you to set a persistent storage for logs.

To get rid of the warning message, you have to edit the advanced settings and manually configure the scratch partition or move the logs to another location:

To configure the scratch partition, it is necessary to have a VMFS or NFS volume attached to the server to host the log files, but of course you would have that anyway, for your VM to live on.

Perform the steps as follows:

1. Access ESXi using the vSphere Client and click the Manage item.
2. Go to the System tab and select Advanced settings to access the advanced settings.

3. In the Search field, type scratch, then press Enter to find the parameter key needed to modify the partition location. The scratchConfig.CurrentScratchLocation contains the current location of the scratch partition. Edit the key ScratchConfig.ConfiguredScratchLocation and enter a unique directory path for this host, for instance, /vmfs/volumes/DatastoreUUID/DatastoreFolder:

4. Reboot the host for the changes to take effect.

Messages from the VMkernel and other system components useful to identify the status of the host or potential issues are written to the log by the ESXi’s syslog service, vmsyslogd.

To modify or configure the log location, you should perform the following steps:

1. Open the vSphere Client and select Manage.
2. Go to the System tab and click Advanced settings under System.

3. Search for the Syslog.global.logDir key that specifies where the logs are stored. The /scratch directory can be located on mounted NFS or VMFS volumes using the syntax [datastorename] path_to_file, where the path is relative to the root of the volume backing the datastore. An entry such as [ts421] /lab-esxi01/logs maps the /vmfs/volumes/ts421/logs path:

4. Click OK to save the configuration. Changes to the syslog options take effect immediately.