Technical Guide Book for PowerVault MD3200MD3220
application. A given host can concurrently have virtual disks with different capacities, different RAID
levels, and different physical disk types. This flexibility enables hosts with different capacity, performance
or data protection demands to effectively share a single storage array.
Snapshot
The MD3200 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
S n a p s h o t
S o u r c e
data mining – while the production data remains
V i r t u a l
V i r t u a l
D i s k
online and user-accessible.
D i s k
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
S n a p s h o t
less disk space. Snapshots appear and function as
R e p o s i t o r y
standard virtual disks; they are host-addressable and
can be read, written to or copied.
L o g i c a l
P h y s i c a l
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 MD3200 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
PiT
B a s e
V i r t u a l
disk is a unique entity that can be assigned to any host and
Clone
V i r t u a l
d i s k C o p y
used by applications requiring a point-in-time (PiT) copy of
d i s k
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
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