6.7

Procedure
1 Obtain the total number of blocks written to the flash device since the last reboot.
Run the esxcli storage core device stats get -d=device_ID command. For example:
~ # esxcli storage core device stats get -d t10.xxxxxxxxxxxxxxx
Device: t10.xxxxxxxxxxxxxxx
Successful Commands: xxxxxxx
Blocks Read: xxxxxxxx
Blocks Written: 629145600
Read Operations: xxxxxxxx
The Blocks Written item in the output shows the number of blocks written to the device since the last
reboot. In this example, the value is 629,145,600. After each reboot, it resets to 0.
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 Written 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 flash device will be
approximately 3.3 years.
About Virtual Flash Resource
You can aggregate local flash devices on an ESXi host into a single virtualized caching layer called virtual
flash resource.
When you set up the virtual flash resource, you create a new file system, Virtual Flash File System
(VFFS). VFFS is a derivative of VMFS, which is optimized for flash devices and is used to group the
physical flash 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 flash resource:
n
Virtual machine read cache. See Chapter 16 About VMware vSphere Flash Read Cache.
n
Host swap cache. See Configure Host Swap Cache with Virtual Flash Resource.
vSphere Storage
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