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vSphere Flash Read Cache FAQ (2057157)

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Purpose

This article provides answers to the frequently asked questions about vSphere Flash Read Cache (vFRC) in vSphere 5.5.

For more information on vSphere Flash Read Cache, see About VMware vSphere Flash Read Cache in vSphere 5.5 Storage guide.

Resolution

Q: Can I partition my SSD and use half for vFRC and half for VMFS?

A: No, the Virtual Flash File System (VFFS) cannot co-exist with any other file system. If there are any existing partitions on the disk, they must be destroyed before configuring vFRC.

 
Q: Can I store a virtual machine in the VFFS?

A: No, it is a non-persistent resource and, therefore, virtual machines cannot be stored in the VFFS.
 
 
Q: Can I share a vSphere Flash Read cache file with multiple virtual machines?

A: No, each cache file is specific to the virtual disk (vmdk) to which it is assigned.
 
 
Q: When I migrate a virtual machine configured with a vSphere Flash Read cache, will the cache be migrated?

A: Yes, if the Always migrate the cache contents option is selected in Select Virtual Flash Migration Settings.


Q: Can I use vSphere Flash Read Cache with VMware vSAN?

A: Yes, however a virtual machine disk file (VMDK) that is located on a vSAN datastore cannot use vSphere Flash Read Cache.
 
Q: Why is the Virtual Machine's first read happening from the disk even if the content is available in the virtual Flash ?

A: Though the vFRC uses a write through cache technique, it is only a read only cache. This means the first read is done from the Disk and written in to the Flash. Later the same data is read from the vFRC.

 
Q: Is there a Hardware Compatibility List for vSphere Flash Read Cache compatible SSD disks?
 
A: Yes, You can refer the VMware HCL guide for vFRC. 

Update History

11/28/2013 - Added additional FAQ related to vSAN

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