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How Snapshot (Legacy) Works
Table 14 Components of a Snapshot (Legacy) Volume
Based on information that you provide through the script commands, the storage
management software creates an empty snapshot (legacy) repository volume and
defines the mapping from a base volume to the snapshot (legacy) repository volume.
The snapshot (legacy) repository volume holds changed data that a host writes to the
base volume. When the snapshot (legacy) repository volume is first created, it holds
only the metadata about the snapshot (legacy) volume with which it is associated.
NOTE
When you first create a snapshot (legacy) repository volume, briefly stop all
of the write operations to the base volume so that a stable image of the base volume is
available.
When the host writes to the base volume, the new data is also copied to the snapshot
(legacy) repository volume. This action is called
copy-on-write
. A snapshot (legacy)
is constructed by combining the updated data in the snapshot (legacy) repository
volume with data in the base volume that has not been altered. This action creates a
complete copy of the base volume at a specific point in time. The snapshot (legacy)
appears as a volume that contains the original data at the time of creation, but the
snapshot (legacy) is actually an image that is the combination of the snapshot (legacy)
repository volume and the original base volume. The snapshot (legacy) repository
volume, which houses original data that has been changed, is the only additional drive
space that is needed for the snapshot (legacy) volume. The additional drive space is
typically 10 percent to 20 percent of the drive space of the base volume and varies
depending on the amount of changes to the data. The longer a snapshot (legacy)
volume is active, the larger the snapshot (legacy) repository volume must be. The
default size of the snapshot (legacy) repository volume is 20 percent of the base
volume; however, you can set the size of the snapshot (legacy) repository volume to
other values.
You can read, write, and copy a snapshot (legacy) volume. Data written by a host to
the snapshot (legacy) volume is handled in the snapshot (legacy) repository volume.
When a write occurs to the base volume of a snapshot (legacy) volume, the new data
also overwrites the appropriate snapshot (legacy) repository volume data.
Component
Description
Base volume
A standard volume from which the snapshot (legacy) is
created
Snapshot (Legacy) volume
A logical point-in-time image of a standard volume
Snapshot (Legacy) repository
volume
A volume that contains snapshot (legacy) metadata and
copy-on-write data for a particular snapshot (legacy)
volume
Содержание InfiniteStorage 4000 Series
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