6.5.1

Table Of Contents
When you enable Flash Read Cache, you can specify the block size and cache size reservation.
Block size is the minimum number of contiguous bytes that can be stored in the cache. This block size
can be larger than the nominal disk block size of 512 bytes, between 4 KB and 1024 KB. If a guest
operating system writes a single 512-byte disk block, the surrounding cache block size bytes are cached.
Do not confuse the cache block size with the disk block size.
Reservation is a reservation size for cache blocks. There is a minimum number of 256 cache blocks. If
the cache block size is 1 MB, then the minimum cache size is 256 MB. If the cache block size is 4 K, then
the minimum cache size is 1 MB.
For more information about sizing guidelines, search for the Performance of vSphere Flash Read Cache
in VMware vSphere white paper on the VMware website.
Prerequisites
Set up virtual flash resource.
Procedure
1 Navigate to the virtual machine.
2 Right-click the virtual machine and select Edit Settings.
3 On the Virtual Hardware tab, expand Hard disk to view the disk menu items.
4 To enable Flash Read Cache for the virtual machine, enter a value in the Virtual Flash Read Cache
text box.
5 Click Advanced to specify the following parameters.
Parameter Description
Reservation Select a cache size reservation.
Block Size Select a block size.
6 Click OK.
Converting Virtual Disks from Thin to Thick
You can determine whether a virtual disk is in the thin provision format and if required, convert it to the
thick provision format.
For more information on thin provisioning and available disk formats, see the vSphere Storage
documentation.
Determine the Disk Format of a Virtual Machine in the vSphere Web Client
You can determine whether your virtual disk is in thick or thin format.
If you have thin provisioned disks, you can change them to thick by selecting Flat pre-initialized disk
provisioning. You change thick provisioned disks to thin by selecting Allocate and commit space on
demand.
vSphere Virtual Machine Administration
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