Glossary

C

changed block tracking (CBT)

A VMware feature that keeps track of which blocks in a virtual disk changed since the time of inception, or when CBT was last enabled. Developers of backup and recovery software can use the CBT feature to help reduce data size for differential or incremental backup.

D

differential backup

Saving system data changed since the last full backup, so only two restore steps are necessary.

E

extent

In the context of VMDK, a split portion of virtual disk, usually 2GB.

F

flat

Space in a VMDK is fully allocated at creation time (pre-allocated). Contrast with sparse.

H

hosted disk

A virtual disk stored on a hosted product, such as VMware Workstation, for its guest operating system.

I

incremental backup

Saving system data changed since the last backup of any type.

M

managed disk

A virtual disk managed by an ESXi host or VMware vCenter, contained within a VMFS volume.

monolithic

The virtual disk is a single VMDK file, rather than a collection of 2GB extents. Contrast with split.

N

NBDSSL

Network block device, a standard method for over-the-network access, with SSL encryption.

P

proxy

A physical or virtual machine running an operating system with third-party backup software. The proxy is used to perform file-level and image-level virtual machine backups.

Q

quiescing

A method of bringing the on-disk data of a physical or virtual computer into a state suitable for backups. Quiescing may include flushing disk buffers from the operating system’s in-memory cache or other tasks.

R

RDM (Raw Device Mapping)

Enables a virtual machine to directly access a LUN on the physical storage subsystem (SAN connected by Fibre Channel, iSCSI, or SAS). At the same time, the virtual machine has access to the disk that is using a mapping file in the VMFS name space. Performance is similar to VMDK.

S

sparse

Space in a VMDK is allocated only when needed to store data. Contrast with flat.

split

The virtual disk is a collection of VMDK files containing 2GB extents. Contrast with monolithic.

V

VMDK (Virtual Machine DisK)

The virtual counterpart to a guest operating system’s physical disk. A file or group of files that can reside on the host machine or on a remote file system.

VMFS (Virtual Machine File System)

A file system optimized for storing virtual machines. One VMFS partition is supported for each SCSI storage device or LUN.

VMX (virtual machine configuration file)

A file containing a virtual machine’s configuration. This .vmx file is created with its virtual machine and is used to identify and run a specific virtual machine.