Dell MD3200i Specifications download pdf (Page 33)

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

Source

Virtual

Disk

Physical

Snapshot

Virtual

Disk

Snapshot

Repository

Logical

Base

Virtual

disk

Virtual

disk

Copy

PiT

Clone

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Dell MD3200i Specifications Page 33

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