vsphere-esxi-vcenter-server-55-storage-guide

Chapter 18 Solid State Disks EnablementBest Practices for SSD DevicesFollow these best practices when you use SSD devices in vSphere environment.• Make sure to use the latest firmware with SSD devices. Frequently check with your storage vendors forany updates.• Carefully monitor how intensively you use the SSD device and calculate its estimated lifetime. Thelifetime expectancy depends on how actively you continue to use the SSD device.Estimate SSD LifetimeWhen working with SSDs, monitor how actively you use them and calculate their estimated lifetime.Typically, storage vendors provide reliable lifetime estimates for an SSD under ideal conditions. Forexample, a vendor might guarantee a lifetime of 5 years under the condition of 20GB writes per day.However, the more realistic life expectancy of the SSD will depend on how many writes per day your hostactually generates. Follow these steps to calculate the lifetime of the SSD.Procedure1 Obtain the number of writes on the SSD by running theesxcli storage core device stats get -d=device_ID command.The Write Operations item in the output shows the number. You can average this number over a periodof time.2 Estimate lifetime of your SSD by using the following formula:vendor provided number of writes per day times vendor provided life span divided by actual average number ofwrites per dayFor example, if your vendor guarantees a lifetime of 5 years under the condition of 20GB writes perday, and the actual number of writes per day is 30GB, the life span of your SSD will be approximately3.3 years.Swapping to Host CacheYou can create VMFS datastores on solid state drives (SSD), and then use these datastores to allocate spacefor host cache. The host reserves a certain amount of space for swapping to host cache.The host cache is made up of files on a low-latency disk that ESXi uses as a write back cache for virtualmachine swap files. The cache is shared by all virtual machines running on the host. Host-level swapping ofvirtual machine pages makes the best use of potentially limited SSD space.Using swap to host cache is not the same as placing regular swap files on SSD-backed datastores. Even ifyou enable swap to host cache, the host still needs to create regular swap files. However, when you useswap to host cache, the speed of the storage where the host places regular swap files is less important.The Host Cache Configuration page allows you to view the amount of space on a datastore that a host canuse to swap to host cache. Only SSD-backed datastores appear in the list of datastores on the Host CacheConfiguration page.If you have a virtual flash license, you can use virtual flash resource to configure cache on the host. For moreinformation, see the vSphere Storage guide for ESXi 5.5.VMware, Inc. 169