Silicon Graphics InfiniteStorage 4000 Series, Configuring And Maintaining

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100 Differences Between Snapshots (Legacy) and Snapshot Image Operations

Identifying the volume group or disk pool in which you want to place the
repository volume

The capacity for the repository volume
You can delete older snapshot images in a snapshot group. When a snapshot image is
deleted, its definition is removed from the system, and the space occupied by the
snapshot image in the repository is released and made available for reuse within the
snapshot group.
You can roll back data by performing one of these actions:

Creating a snapshot volume of a snapshot image, which enables you to retrieve
deleted files from that snapshot volume (the base volume remains undisturbed).

Restoring a snapshot image to the base volume, which enables you to roll back
the base volume to a previous state.
Characteristics of Snapshot Images

Snapshot images are always created inside snapshot groups.

Each snapshot image is associated with exactly one snapshot group.

There is a maximum limit of snapshot groups for a single associated base volume
(depending on your configuration).

There is a maximum limit of snapshot images per snapshot group (depending on
your configuration).
Differences
Between
Snapshots
(Legacy) and
Snapshot Image
Operations A snapshot image is a logical point-in-time image of a volume. The snapshot image
feature is similar to the snapshot (legacy) feature, with the following differences:

The new snapshot image feature offers improved performance when a base
volume has multiple point-in-time images. The snapshot (legacy) feature uses
one data repository for each snapshot (legacy) volume. The new snapshot image
feature uses one data repository for all of the snapshot images associated with a
base volume. Therefore, when a base volume is written to, the new snapshot
image feature requires only one write operation instead of multiple, sequential
write operations.

The new snapshot image feature adds the concept of a snapshot group. Because
there is only one repository for multiple snapshot images, the repository is
associated with the snapshot group instead of with the snapshot image as it is
with the snapshot (legacy) feature.

Unlike a snapshot (legacy) volume, a new snapshot image is not directly
read-write
accessible by hosts because the snapshot image is used only to
save the changed data for a base volume. To provide hosts with
read-write
access to a snapshot image, you must first create a snapshot volume.

You can create either snapshots (legacy) or snapshot images from a base volume,
but not both.