## 10.2 Virtual Flash Memory 

This section provides information about the configuration of the Virtual Flash Memory (VFM) feature on an IBM z15. It covers the following topics: 

## 10.2.1 VFM overview 

GLYPH<SM590000> VFM overview 

GLYPH<SM590000> Planning for VFM configuration 

GLYPH<SM590000> Configuring VFM 

GLYPH<SM590000> VFM management 

The VFM is the replacement for the Flash Express features that were available on the zEC12, zBC12, z13, and z13s. VFM offers up to 6.0 TB of virtual flash memory in 512 GB increments. No application changes are required to change from Flash Express to VFM. 

VFM is designed to help improve availability and handling of paging workload spikes when running z/OS V2.1, V2.2, z/OS V2.3, or V2.4. With this support, z/OS is designed to help improve system availability and responsiveness by using VFM across transitional workload events such as market openings, and diagnostic data collection. z/OS is also designed to help improve processor performance by supporting middleware exploitation of pageable large (1 MB) pages. 

Using VFM can help availability by reducing latency from paging delays that can occur at the start of the workday or during other transitional periods. It is also designed to help eliminate delays that can occur when collecting diagnostic data during failures. VFM can also be used in coupling facility images to provide extended capacity and availability for workloads making use of IBM WebSpherefi MQ Shared Queues structures. 

VFM can help organizations meet their most demanding service level agreements and compete more effectively. VFM is designed to be easy to configure, and to provide rapid time to value. 

For more information about the VFM feature, see the IBM z15 Technical Guide , SG24-8851. 

## 10.2.2 Planning for VFM configuration 

For planning considerations, see “Planning considerations for Virtual Flash Memory” on page 19. 

## 10.2.3 Configuring VFM 

The Assignment of VFM to LPARs is exclusively done with the definitions in the image activation profiles. 

Note:  Unlike the Flash Express cards, the allocation of VFM to LPARs cannot be altered to an activated LPAR. So the Manage Flash Allocation  selection on the HMC is not supported for z15. 

