Dell PowerVault MD3220i Series Buku Panduan Teknis - Halaman 33
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DELL PowerVault MD3200i/MD3220i Technical Guide Book
Snapshot
The MD3200i series of arrays Snapshot functionality provides
an additional level of data protection and the means to
improve production data utilization. Snapshot enables non-
production servers to access an up-to-date copy of production
data for a variety of applications – including backup,
application testing, or data mining – while the production data
remains online and user-accessible.
A snapshot is a point-in-time image of a source virtual disk. It
is the logical equivalent of a complete physical copy, but is
created much more quickly and requires less disk space.
Snapshots appear and function as standard virtual disks; they
are host-addressable and can be read, written to or copied.
Snapshot uses an innovative copy-on-write technology to
maintain the logical snapshot virtual disk while minimizing
disk utilization. When the snapshot is "taken," the controller
suspends I/O to the source virtual disk for a few seconds while
it creates a new physical virtual disk – called the repository virtual disk – to store snapshot metadata
and copy-on-write data. When a data block on the source virtual disk is modified, a copy-on-write
occurs, copying the contents of blocks that are to be modified into the repository virtual disk for
safekeeping. This repository virtual disk combined with the original source virtual disk creates the
logical snapshot virtual disk.
Since the only data blocks that are physically stored in the repository virtual disk are those that have
changed since the time of the snapshot, the snapshot technology uses less disk space than a full
physical copy. The repository virtual disk is typically 20 percent of the base virtual disk, but will vary
depending on the amount of changes to the data. The longer a snapshot is active, the larger the
repository is needed. Virtual disk snapshot provides notification when the repository virtual disk nears a
user-specified threshold (a percentage of its full capacity). And at any time, the volume expansion
feature can be used to dynamically expand the repository virtual disk.
Virtual Disk Copy
The MD3200i series of arrays Virtual Disk Copy functionality provides administrators with another tool
to effectively manage information growth and maximize the utilization of the storage array. Virtual
disk copy creates a complete physical copy, or a clone, of a virtual disk within a storage array. The
clone virtual disk is a unique entity that can be assigned to any host and used by applications requiring
a point-in-time (PiT) copy of production data – such as backup,
application testing or development, information analysis or
data mining – without affecting the performance of the
production virtual disk.
Virtual disk copy is configured and accessed via easy-to-use
wizards. It supports up to eight concurrent copies taking place
within a single array. Virtual disk copy is a background
operation with five user-defined priority settings, enabling
administrators to minimize either copy time or the overall I/O
impact to the storage system. As virtual disk copy is controller
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