A
Asynchronous Replication
After data has been written to the primary storage site, new writes to that site can be accepted, without having to wait for the secondary (remote) storage site to also finish its writes. Asynchronous Replication does not have the latency impact that synchronous replication does, but has the disadvantage of incurring data loss, should the primary site fail before the data has been written to the secondary site. See also replication.
Asynchronous replication Asynchronous replication confirms to the originating host that the primary I/O transaction is complete before updating the remote image. That is, completion of the I/O transaction is acknowledged to the host when the local write operation is finished and the remote write operation has been queued.
AAA
(Authentication Authorization Accounting server) A network server used for access control. Authentication identifies the user. Authorization implements policies that determine which resources and services a valid user may access. Accounting keeps track of time and data resources used for billing and analysis. See RADIUS, authentication server and access control.
B
In data restoration, the backup window is a predetermined amount of time in which specific data must be restored to avoid any negative or damaging effects on the systems or applications that use the data.
C
CIFS
Common Internet File System, a protocol that defines a standard for remote file access using millions of computers at a time. With CIFS, users with different platforms and computers can share files without having to install new software.
CIFS runs over TCP/IP but uses the SMB (Server Message Block) protocol found in Microsoft Windows for file and printer access; therefore, CIFS will allow all applications, not just Web browsers, to open and share files across the Internet.
D
DAS (Direct Attached Storage)
DAS is storage that is directly connected to a server by connectivity media such as parallel SCSI cables. This direct connection provides fast access to the data; however, storage is only accessible from that server. DAS include the internally attached local disk drives or externally attached RAID (redundant array of independent disks) or JBOD (just a bunch of disks). Although Fibre Channel can be used for direct attached, it is more commonly used in storage area networks.
Data De-duplication
In storage technology, deduplication essentially refers to the elimination of redundant data. In the deduplication process, duplicate data is deleted, leaving only one copy of the data to be stored. However, indexing of all data is still retained should that data ever be required. Deduplication is able to reduce the required storage capacity since only the unique data is stored. Deduplication is also also written as de-duplication, and is synonymous with data reduction or commonality factoring
DFS (Distributed File System)
DFS allows administrators to group shared folders located on different servers by transparently connecting them to one or more DFS namespaces. A DFS namespace is a virtual view of shared folders in an organization.
Disaster Recovery
The ability to recover from the loss of a complete site, whether due to natural disaster or malicious intent. Disaster recovery strategies include replication and backup/restore.
Dynamic Disk
A dynamic disk is a physical disk that provides features that basic disks do not, such as support for volumes spanning multiple disks. Dynamic disks use a hidden database to track information about dynamic volumes on the disk and other dynamic disks in the computer.
DWDM
Short for Dense Wavelength Division Multiplexing, an optical technology used to increase bandwidth over existing fiber optic backbones.
DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. In effect, one fiber is transformed into multiple virtual fibers. So, if you were to multiplex eight OC -48 signals into one fiber, you would increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s. Currently, because of DWDM, single fibers have been able to transmit data at speeds up to 400Gb/s.
A key advantage to DWDM is that it's protocol- and bit-rate-independent. DWDM-based networks can transmit data in IP, ATM, SONET /SDH, and Ethernet, and handle bit rates between 100 Mb/s and 2.5 Gb/s. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel.
From a QoS standpoint, DWDM-based networks create a lower cost way to quickly respond to customers' bandwidth demands and protocol changes.
E
Enterprise Systems Connection
A 200 Mbps serial I/O bus used on IBM Corporation’s Enterprise System 9000 data center computers. Abbreviated ESCON. Similar to Fibre Channel in many respects, ESCON is based on redundant switches to which computers and storage subsystems connect using serial optical connections.
F
Fabric
A Fibre Channel (or iSCSI) topology with at least one switch present on the network.
Failover
In the event of a physical disruption to a network component, data is immediately rerouted to an alternate path so that services remain uninterrupted. Failover applies both to clustering and to multiple paths to storage. In the case of clustering, one or more services (such as Exchange) is moved over to a standby server in the event of a failure. In the case of multiple paths to storage, a path failure results in data being rerouted to a different physical connection to the storage.
Fault–Tolerance
Fault–tolerance is the ability of computer hardware or software to ensure data integrity when hardware failures occur. Fault-tolerant features appear in many server operating systems and include mirrored volumes, RAID– volumes, and server clusters.
FC-IP
FC-IP enables organizations to bridge Fibre Channel Storage Area Networks (SANs) deployed in remote sites using FCIP connectivity. Utilizing IP networks, companies can ensure timely access to mission-critical data and provide business continuity and disaster recovery over metro and wide area networks.
The FCIP router is a reliable, dedicated solution that provides continuous access to remote Fibre Channel SANs for critical applications such as mirroring, data replication and backup. The FCIP router utilizes an architecture specifically designed for FCIP protocol transmission over TCP/IP networks. Hardware-based compression ensures full WAN utilization up to T3 line rates resulting in significant cost savings
Fibre Channel Arbitrated Loop. (FC-AL)
Fibre Channel-Arbitrated Loop. A Fibre Channel implementation where users are attached to a network via a one-way ring (loop) cabling scheme.
Failover
The automatic substitution of a functionally equivalent system component for a failed one. The term failover is most often applied to intelligent controllers connected to the same storage devices and host computers. If one of the controllers fails, failover occurs, and the survivor takes over its I/O load.
Fibre Channel
A high–speed interconnect used in storage area networks (SANs) to connect servers to shared storage. Fibre Channel components include HBAs, hubs, switches, and cabling. The term Fibre Channel also refers to the storage protocol.
FRS
File Replication service (FRS) is a technology that replicates files and folders stored in the SYSVOL shared folder on domain controllers and Distributed File System (DFS) shared folders. When FRS detects that a change has been made to a file or folder within a replicated shared folder, FRS replicates the updated file or folder to other servers.
Full synchronization
Full synchronization performs a complete volume-to-volume copy, which is the most time-consuming of the synchronization operations. In most cases, a secondary volume is synchronized from its source primary volume. However, restoration of a failed primary disk might require reverse synchronization, using the surviving remote mirror as the source.
H
High Availability
A continuously available computer system is characterized as having essentially no downtime in any given year. A system with 99.999% availability experiences only about five minutes of downtime. In contrast, a high availability system is defined as having 99.9% uptime, which translates into a few hours of planned or unplanned downtime per year.
HBA (Host Bus Adapter)
The HBA is the intelligent hardware residing on the host server which controls the transfer of data between the host and the target storage device.
I
Initiator
An initiator is the device (usually contained within a server) that makes the application requests; which are then sent to the target device.
iSCSI (Internet SCSI)
A protocol that enables transport of block data over IP networks, without the need for a specialized network infrastructure, such as Fibre Channel.
J
JBOD (Just a Bunch of Disks)
As the name suggests, a group of disks housed in its own box; JBOD differs from RAID in not having any storage controller intelligence or data redundancy capabilities.
L
Load Balancing
Referring to the ability to redistribute load (read/write requests) to an alternate path between server and storage device, load balancing helps to maintain high performance networking.
LUN (Logical Unit Number)
A logical unit is a conceptual division (a subunit) of a storage disk or a set of disks. Logical units can directly correspond to a volume drive (for example, C: can be a logical unit). Each logical unit has an address, known as the logical unit number (LUN), which allows it to be uniquely identified.
LUN Masking
A method to restrict server access to storage not specifically allocated to that server. LUN masking is similar to zoning, but is implemented in the storage array, not the switch.
M
Mount Point
A mount point is a directory on a volume that an application can use to "mount" (set up for use) a different volume. Mount points overcome the limitation on drive letters and allow more logical organization of files and folders.
Multipathing
Multipathing is the use of redundant storage network components responsible for transfer of data between the server and storage. These components include cabling, adapters and switches and the software that enables this.
Multithreading
The ability of an operating system to execute different parts of a program, called threads, simultaneously. The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other.
N
NAS (Network Attached Storage)
A NAS device is a server that runs an operating system specifically designed for handling files (rather than block data). Network-attached storage is accessible directly on the local area network (LAN) through LAN protocols such as TCP/IP. Compare to DAS and SAN.
NTFS File System
A file system that provides performance, security, reliability, and advanced features that are not found in any version of the file allocation table (FAT) filesystem. For example, NTFS guarantees volume consistency by using standard transaction logging and recovery techniques. If a system fails, NTFS uses its log file and checkpoint information to restore the consistency of the file system. NTFS also provides advanced features, such as file and folder permissions, encryption, disk quotas, and compression.
NIS
The Network Information Service or NIS (originally called Yellow Pages or YP) consists of a client-server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network. Sun Microsystems developed the NIS and licenses this technology to virtually all other Unix vendors.
An NIS/YP system maintains and distributes a central directory of user and group information, hostnames, e-mail aliases and other text-based tables of information in a computer network. For example, in a common UNIX environment, the list of users for identification is placed in /etc/passwd, and secret authentication hashes in /etc/shadow. NIS adds another “global” user list which is used for identifying users on any client of the NIS domain.
P
Partition
A partition is the portion of a physical disk or LUN that functions as though it were a physically separate disk. Once the partition is created, it must be formatted and assigned a drive letter before data can be stored on it. On basic disks, partitions can contain basic volumes, which include primary partitions and logical drives. On dynamic disks, partitions are known as dynamic volumes, which include simple, striped, spanned, mirrored, and RAID–5 (striped with parity) volumes.
Port
The physical connection point on computers, switches, storage arrays, etc, which is used to connect to other devices on a network. Ports on a Fibre Channel network are identified by their Worldwide Port Name (WWPN) IDs; on iSCSI networks, ports are commonly given an iSCSI name. Not to be confused with TCP/IP ports, which are used as virtual addresses assigned to each IP address.
R
RAID (Redundant Array of Independent Disks)
A way of storing the same data over multiple physical disks to ensure that if a hard disk fails a redundant copy of the data can be accessed instead. Example schemes include mirroring and RAID–5.
Redundancy
The duplication of information or hardware equipment components to ensure that should a primary resource fail, a secondary resource can take over its function.
Replication
Replication is the process of duplicating mission critical data from one highly available site to another. The replication process can be synchronous or asynchronous; duplicates are known as clones, point-in-time copies, or snapshots, depending on the type of copy being made.
S
SAN (Storage Area Network)
A storage area network (SAN) is a specialized network that provides access to high performance and highly available storage subsystems using block storage protocols. The SAN is made up of specific devices, such as host bus adapters (HBAs) in the host servers, switches that help route storage traffic, and disk storage subsystems. The main characteristic of a SAN is that the storage subsystems are generally available to multiple hosts at the same time, which makes them scalable and flexible. Compare with NAS and DAS.
SCSI (Small Computer System Interface)
A set of standards allowing computers to communicate with attached devices, such as storage devices (disk drives, tape libraries etc) and printers. SCSI also refers to a parallel interconnect technology which implements the SCSI protocol.
Shadow Copy
A shadow copy is a high fidelity point–in–time copy of the original data. In the Windows environment, shadow copies are created using the Volume Shadow Copy Service (VSS); third party applications can create shadow copies also.
Snapshot
[Data Recovery] [Storage System] A fully usable copy of a defined collection of data that contains an image of the data as it appeared at the point in time at which the copy was initiated.
Storage Array
A subsystem which houses a group of disks (or tapes), together controlled by software usually housed within the subsystem.
Storage Controller
Providing such functionality as disk aggregation (RAID), I/O routing, and error detection and recovery, the controller provides the intelligence for the storage subsystem. Each storage subsystem contains one or more storage controllers.
Switch
An intelligent device residing on the network responsible for directing data from the source (such as a server) or sources directly to a specific target device (such as a specific storage device) with minimum delay. Switches differ in their capabilities; a director class switch, for example, is a high end switch that provide advanced management and availability features.
Synchronous Replication
In synchronous replication, each write to the primary disk and the secondary (remote) disk must be complete before the next write can begin. The advantage of this approach is that the two sets of data are always synchronized. The disadvantage is that if the distance between the two storage disks is substantial, the replication process can take a long time and slows down the application writing the data. See also asynchronous replication.
T
Target
A target is the device to which the initiator sends data. Most commonly the target is the storage array, but the term also applies to bridges, tape libraries, tape drives or other devices.
Tiered Storage
Data is stored according to its intended use. For instance, data intended for restoration in the event of data loss or corruption is stored locally, for fast recovery. Data required to be kept for regulatory purposes is archived to lower cost disks.
V
VDS (Virtual Disk Service)
VDS is a set of application programming interfaces (APIs) that provides a single interface for managing disks in Windows Server 2003 operating systems. VDS provides a means of managing storage hardware and disks, and for creating volumes on those disks.
Virtualization
In storage, virtualization is a means by which multiple physical storage devices are viewed as a single logical unit. Virtualization can be accomplished in–band (in the data path) or out-of-band. Out–of–band virtualization does not compete for host resources, and can virtualize storage resources irrespective of whether they are DAS, NAS or SAN.
Volume
A volume is an area of storage on a hard disk. A volume is formatted by using a file system, such as file allocation table (FAT) or NTFS, and typically has a drive letter assigned to it. A single hard disk can have multiple volumes, and volumes can also span multiple disks.
VSS (Volume Shadow Copy Service)
The Volume Shadow Copy Service provides the backup infrastructure for the Microsoft Windows XP and Microsoft Windows Server 2003 operating systems, as well as a mechanism for creating consistent point-in-time copies of data known as shadow copies.
Z
Zoning
A method used to restrict server access to storage resources that are not allocated to that server. Zoning is similar to LUN masking, but is implemented in the switch and operates on the basis of port identification (either port numbers on the switch or by WWPN of the attached initiators and targets).
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