Tru64 Unix Host Volumes; Types - HP 418800-B21 - StorageWorks Modular Smart Array 70 Storage Enclosure User Manual

• Demand allocated. The space allocated for the snapshot can automatically change from an initial
minimum amount, up to the full capacity of the original (active) virtual disk.
• Fully allocated. The space allocated for the snapshot is initially set to, and remains fixed at, the
full capacity of the source (active) virtual disk.
Demand-allocated snapshots
When a snapshot is demand allocated, the storage system initially allocates only a small amount of
space for the snapshot, just enough to store point-in-time information and pointers to data on the source.
As data on the source is over-written, the controller increases the allocated space for the snapshot and
copies the original (point-in-time) data from the source to the snapshot.
If all the original data on the source is over-written, the controller increases the allocated space on the
snapshot by an amount equal 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 initially allocates an amount of space that is equal
to the capacity of the source virtual disk, plus a small amount of space for point-in-time information and
pointers to data on the source. As data is over-written on the source, the controller copies the original
(point-in-time) data from the source to the snapshot. The amount of space allocated on the snapshot
never changes.
Once created, a fully allocated snapshot cannot run out of space.

Tru64 UNIX host volumes

General
• The replication manager displays information about UFS, AdvFS host volumes and LSM logical
volumes on enabled hosts.
• In a host cluster, only the volumes on the cluster's enabled host are displayed. See
• Local replication of UFS and AdvFS host volumes is supported. Local replication of LSM logical
volumes is not supported. See
Mounting
• The replication manager does not support mounting a Tru64 host volume in a subdirectory of
/tmp.

Types

Virtual disks types reported by the replication manager:
442
Virtual disks
local replication.
enabled hosts.