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

vSphere StorageDRS Support for Flash Read CacheDRS supports virtual flash as a resource.DRS manages virtual machines with Flash Read Cache reservations. Every time DRS runs, it displays theavailable virtual flash capacity reported by the ESXi host. Each host supports one virtual flash resource. DRSselects a host that has sufficient available virtual flash capacity to start a virtual machine. DRS treatspowered-on virtual machines with a Flash Read Cache as soft affined to their current host and moves themonly for mandatory reasons or if necessary to correct host over-utilization.vSphere High Availability Support for Flash Read CacheFlash Read Cache is supported by High Availability (HA).When vSphere HA restarts a virtual machine configured with Flash Read Cache, the virtual machine isrestarted on a host in the cluster where the Flash Read Cache, CPU, Memory and overhead reservations aremet. vSphere HA will not restart a virtual machine if unreserved flash is insufficient to meet the virtual flashreservation. You must manually reconfigure a virtual machine to reduce or drop the Flash Read Cache, ifthe target host does not have sufficient virtual flash resource available.Using Virtual Flash Resource to Configure a Swap CacheYou can use virtual flash resource on an ESXi host to configure a swap cache. The host swap cache isallocated from a portion of the virtual flash resource.You can virtualize flash devices on a host to use as a virtual flash resource on that host, regardless of thetype of flash device. Virtual flash does not require every host in the cluster to have flash, but only hosts withflash devices can have cache devices configured. You can use virtual flash with existing VMware solutionssuch as vMotion, DRS and HA.You can configure vSphere to enable ESXi host swapping to a solid-state disk (SSD). In high memory usage,host swapping is used to reclaim memory from virtual machines. vSphere randomly selects the virtualmachine physical pages to be swapped out, compresses memory of the virtual machine pages that aretargeted by ESXi to be swapped out, and lets you configure a swap cache on the SSD.Virtual Flash Volume LimitsThe following virtual flash volume limitations are supported.Table 21‐1. Virtual flash volume limitsResourcevirtual flash volumes per hostSSDs per virtual flash volumeSSD sizevirtual flash sizeLimit1 (local only)8 or fewer4TB or less32TB or lessSet Up Virtual Flash ResourceYou can set up a virtual flash resource or add capacity to existing virtual flash resource.To set up a virtual flash resource you use a solid-state disk (SSD) connected to your host. To increase thecapacity of your virtual flash resource, you can add more SSDs, up to a total of eight. An individual SSDmust be exclusively allocated to a virtual flash resource and cannot be shared with any other vSphereservice, such as Virtual SAN.206 VMware, Inc.