6.0.1

2 Calculate the total number of writes and convert to GB.
One block is 512 bytes. To calculate the total number of writes, multiply the Blocks Wrien value by 512,
and convert the resulting value to GB.
In this example, the total number of writes since the last reboot is approximately 322 GB.
3 Estimate the average number of writes per day in GB.
Divide the total number of writes by the number of days since the last reboot.
If the last reboot was ten days ago, you get 32 GB of writes per day. You can average this number over
the time period.
4 Estimate lifetime of your device by using the following formula:
vendor provided number of writes per day times vendor provided life span divided by actual average number of
writes per day
For example, if your vendor guarantees a lifetime of 5 years under the condition of 20 GB writes per
day, and the actual number of writes per day is 30 GB, the life span of your ash device will be
approximately 3.3 years.
About Virtual Flash Resource
You can aggregate local ash devices on an ESXi host into a single virtualized caching layer called virtual
ash resource.
When you set up the virtual ash resource, you create a new le system, Virtual Flash File System (VFFS).
VFFS is a derivative of VMFS, which is optimized for ash devices and is used to group the physical ash
devices into a single caching resource pool. As a non-persistent resource, it cannot be used to store virtual
machines.
The following vSphere functionalities require the virtual ash resource:
n
Virtual machine read cache. See Chapter 15, “About VMware vSphere Flash Read Cache,” on page 141.
n
Host swap cache. See “Congure Host Swap Cache with Virtual Flash Resource,” on page 140.
n
I/O caching lters, if required by your vendors. See Chapter 21, “Filtering Virtual Machine I/O,” on
page 243.
Before seing up the virtual ash resource, make sure that you use devices approved by the VMware
Compatibility Guide.
Considerations for Virtual Flash Resource
When you congure a virtual ash resource that is consumed by ESXi hosts and virtual machines, several
considerations apply.
n
You can have only one virtual ash resource, also called a VFFS volume, on a single ESXi host. The
virtual ash resource is managed only at the host's level.
n
You cannot use the virtual ash resource to store virtual machines. Virtual ash resource is a caching
layer only.
n
You can use only local ash devices for the virtual ash resource.
n
You can create the virtual ash resource from mixed ash devices. All device types are treated the same
and no distinction is made between SAS, SATA, or PCI express connectivity. When creating the resource
from mixed ash devices, make sure to group similar performing devices together to maximize
performance.
n
You cannot use the same ash devices for the virtual ash resource and Virtual SAN. Each requires its
own exclusive and dedicated ash device.
Chapter 14 Working with Flash Devices
VMware, Inc. 137