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Setting the cache size for virtual machines
When you set the cache size for a virtual machine, you reserve a portion of the flash device on the ESXi host for use as cache by applications running on the virtual machine. Flash Accel performance statistics will tell you whether you have too much or too little cache allocated for a VM.
Before you begin 
The virtual machine must be configured with memory sized appropriately for the cache size, approximately 0.6 GB of RAM for every 100 GB of cache. So if you are planning to provide 250 GB of cache for the virtual machine, you should configure 1.5 GB of RAM (in addition to whatever RAM is required to run the virtual machine and applications).
About this task 
Setting the cache size adds a physical Raw Device Mappings (pRDM) device to the virtual machine as the logical device that represents the cache. The mapping file for this pRDM device is added to the same datastore as the one being used by the virtual machine. This file is fairly small, but you should make sure you are not low on space on the datastore, or the installation could fail.
Note: If the virtual machine is stored on an NFS datastore, the mapping file is stored on a VMFS datastore. If a VMFS datastore is unavailable, you will not be able to allocate cache to the VM.
Steps 
1.
From the Home page of the Flash Accel Management Console, click the wrench icon for the virtual machine on which you want to set the cache size and select Cache Space > Allocate.
The Cache Space dialog box appears.
2.
To enter the cache size manually, click the Enter Manually check box, then enter the cache size in the Enter Cache Space Size field.
Depending on the cache size you specified, formatting the flash device can take five minutes or more. You can monitor the progress of the allocation process in the Ongoing Processes page.
Result 
The Cache Size field for the virtual machine is set to the specified value.
Parent Topic: Getting started with Flash Accel


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