HP 3PAR StoreServ 7450 4-node HP 3PAR StoreServ Storage Concepts Guide (OS 3.1 - Page 39

8 Common Provisioning Groups Overview A common provisioning group (CPG) creates a virtual pool of logical disks that allows virtual volumes to share the CPG's resources and allocates space on demand. You can create fully-provisioned virtual volumes and thinly-provisioned virtual volumes (TPVVs) that draw space from the CPG's logical disk pool. CPGs enable fine-grained, shared access to pooled logical capacity. Instead of pre-dedicating logical disks to volumes, the CPG allows multiple volumes to share the buffer pool of logical disks. For example, when a TPVV is running low on user space, the system automatically assigns more capacity to the TPVV by mapping new regions from logical disks in the CPG associated with that TPVV. As a result, any large pockets of unused but allocated space are eliminated. Fully provisioned virtual volumes cannot create user space automatically and the system allocates a fixed amount of user space for the volume. By default, a CPG is configured to auto-grow new logical disks when the amount of available logical disk space falls below a configured threshold. The initial buffer pool of logical disks starts off at a fraction of the exported virtual capacity of mapped volumes and automatically grows over time as required by application writes. Creating CPGs can be performed with both the HP 3PAR Command Line Interface (CLI) and the HP 3PAR Management Console. Refer to the HP 3PAR Command Line Interface Administrator's Manual and the HP 3PAR Management Console Online Help for instructions on how to perform these tasks. For more information about TPVVs and fully-provisioned virtual volumes, see "Virtual Volumes" (page 42). Precautions and Planning A Common Provisioning Group (CPG) creates a virtual pool of logical disks that allows up to 4,095 volumes to share the CPG's resources and allocate space on demand. However, CPGs still require careful planning and monitoring to prevent them from becoming so large that they set off the system's built-in safety mechanisms. These safety mechanisms are designed to prevent a CPG from consuming all free space on the system, but they only work properly on systems that are planned carefully and monitored closely. The maximum number of CPGs per system is 2,048. Growth Increments, Warnings, and Limits You can create several types of volumes that draw space from the CPG's logical disk pool as needed. When creating a CPG, set a growth increment and an optional growth warning and growth limit to restrict the CPG's growth and maximum size. It is important to plan the CPG's growth increment, growth warning, and growth limit carefully and then continue to monitor the CPG closely over time. CAUTION: Use caution in planning CPGs. The system does not prevent you from setting growth warnings or growth limits that exceed the amount of currently available storage on a system. When volumes associated with a CPG use all space available to that CPG, any new writes to TPVVs associated with the CPG will fail and/or snapshot volumes associated with the CPG may become invalid or stale. Under these conditions, some host applications do not handle write failures gracefully and may produce unexpected failures. NOTE: By default, the growth warning and growth limit are set to none, which effectively disables these safety features. Overview 39