HP 418800-B21 HP StorageWorks Replication Solutions Manager 4.0.1 user guide ( - Page 152

Snapshot lifetime Short Long Estimated changes in source data Less than 25% 25% or more Recommended snapshot type Demand allocated Fully allocated Demand-allocated snapshots When a snapshot is demand allocated, the storage system allocates only enough space to store metadata and pointers to the source data. As the source is overwritten, the array allocates more space and copies the original data to the snapshot. If all the original data on the source is over-written, the controller increases the allocated space on the snapshot to the full size of the source. The size of the disk group in which the source and snapshot are located must be sufficient to handle increases in snapshot size, whenever the increases might occur. Insufficient space in the disk group can not only prevent the controller from increasing the space allocation, but it can also prevent writes to both the source and snapshot. Fully allocated snapshots When a snapshot is fully allocated, the storage system allocates only enough space to store metadata and pointers to the source data, but reserves space equal to the capacity of the source virtual disk. As the source is overwritten, the array allocates more space and copies the original data to the snapshot. Once created, a fully allocated snapshot cannot run out of space. Types (components) The type property indicates the component structure of the host volume. This varies with the host operating system and logical volume manager. Examples: Device. All OSs. Logical volume. AIX, HP-UX, Linux, Solaris, Tru64 UNIX Partition (slice). AIX, HP-UX, Linux, Solaris, Windows. See partitions and slices. Volume set, dynamic disk, spanned volume. Windows Dynamic capacity management Dynamic capacity management overview DC-Management provides you with the capability to extend (increase) or shrink (decrease) the size of a host volume without disrupting host I/O. This gives you greater control over the size of host volumes as your system storage requirements change. If a host volume is nearing capacity, you can extend the size of the volume to avoid the situation that occurs when a host volume reaches its full capacity. If a host volume has too much capacity allocated to it, you can shrink the size of the volume, freeing up the unused capacity for other applications. DC-Management can be implemented manually or automatically. • Manual DC-Management enables you to immediately change the volume size. The new size remains in effect until you manually reset it again. • Automatic DC-Management policies enable you to specify the threshold at which you want the size of the volume to be changed. RSM monitors the capacity of the host volume and automatically changes the size when the specified threshold is reached. You can set e-mail notification alerting you when a volume has been resized. You can also control the time during which the policy is enforced. 152 Host volumes