Copyright © Acronis, Inc., 2000-2010 73
Each non-empty file completely occupies one or more clusters.
The typical size of a cluster is 4 KB. When formatting a volume, you can choose the cluster size for it.
Smaller cluster sizes allow for more efficient storage of smaller files by reducing the amount of
wasted disk space; but larger files may become more fragmented across the volume, which may
increase the amount of time that is needed to access them.
A cluster is also known as an allocation unit.
Physically, a cluster is one or more (usually eight) sectors on a disk.
Cylinder
A group of all tracks (p. 81) on all magnetic platters of a hard disk (p. 76) that can be accessed
without moving the magnetic head.
Access to the data inside one cylinder is much faster than moving the head from one cylinder to
another.
D
Defragmentation
The process of rearranging files on a volume to reduce fragmentation (p. 76), which may improve file
access times.
Disk
A storage device, often a magnetic storage medium, which is attached to a machine.
Examples of disks include hard disks and floppy disks.
Disk group
A number of dynamic disks that store the common configuration data in their Logical Disk Manager
(LDM) databases and therefore can be managed as a whole.
Normally, all dynamic disks created within the same machine are members of the same disk group.
As soon as the first dynamic disk is created by the LDM or another disk management tool, the disk
group name can be found in the registry key
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\dmio\Boot Info\Primary Disk
Group\Name.
The next created or imported disks are added to the same disk group. The group exists as long as at
least one of its members exists. Once the last dynamic disk is disconnected or converted to basic, the
group is discontinued, though its name is kept in the above registry key. In case a dynamic disk is
created or connected again, a disk group with an incremental name is created.
When moved to another machine, a disk group is considered as foreign (p. 76) and cannot be used
until imported into the existing disk group. The import updates the configuration data on both the
local and the foreign disks so that they form a single entity. A foreign group is imported as is (will
have the original name) if no disk group exists on the machine.
