This glossary contains terms related to EMC Symmetrix Solutions Enabler. Many of these terms are used throughout the Solutions Enabler documentation set.

 

A

Access Pool

A set of devices made accessible to a host, whose access is limited by the access rights assigned.

Adaptive Copy – Disk Mode

An SRDF mode of operation designed for transferring large amounts of data without loss of performance. New data for a remotely mirrored pair is stored on the source (R1) device of that pair as invalid tracks. This operation continues until data can be successfully transferred to the target (R2) device.

Adaptive Copy – Write Pending Mode

An SRDF mode of operation where all writes to the source (R1) device is acknowledged as if they were to a local device. New data for a remotely mirrored pair is stored in the cache of the local Symmetrix array until it can be successfully written to both the source (R1) and target (R2) devices.

Asynchronous Mode

See SRDF/A.

B

BCV Device

A Symmetrix business continuance volume (BCV) that functions as a mirrored media to a standard device for a protected storage environment.

BCV Pair

A combination of a standard device and a BCV device that provides a protected storage environment.

Business Continuance

A protected storage environment solution that has defined specially configured Symmetrix devices as mirrors or Business Continuance Volumes (BCVs) to protect data on standard devices.

Business Continuance

Volume (BCV)

See BCV Device.

C

Cache

Randomly accessed, electronic storage used to retain frequently used data from disk for faster access by the channel. On a Symmetrix array, cache memory resides on cards that occupy slots on a Symmetrix backplane. Cache memory buffers I/O transfers between the director channels and the storage devices.

Checksum Checking

A process that checks each RDBMS write in the Symmetrix array, with a checksum value that is computed and compared to test the data for any corruption picked up along the way from the host.

Composite Group

(CG)

A user-defined group of devices that can span multiple Symmetrix arrays and RA groups. The CG type may be defined as REGULAR, RDF1, or RDF2 and may contain various device lists for standard, BCV, virtual (VDEV), and remote BCV devices.

Concatenated Meta

Device

Disk volume sets that are organized and addressed beginning with the first byte of data of the first device, continuing to the end of the first device before any data on the next device is referenced. On writes to a concatenated device, all the data is written to the first meta device member until it is full, and then data is directed to the next member, and so on.

Concurrent RDF

An SRDF configuration where a single source (R1) device is remotely mirrored to two target (R2) devices, allowing identical remote copies to be available at any point in time. Concurrent RDF supports asynchronous, synchronous, semi-synchronous, and adaptive copy SRDF operational modes.

Consistency Group

A composite group that is comprised of RDF devices (RDF1 or RDF2) and has been enabled for RDF consistency. The devices within the RDF consistency group act in unison to preserve dependent write consistency of a database distributed across multiple SRDF systems. Consistency is maintained via PowerPath, which respects the logical relationships between dependant I/O cycles.

D

Daemon

A service that improves performance on a number of applications or scripts running at once. It runs in the background with root privileges to a local Symmetrix storage array.

Data Block

A logical storage structure that is the smallest unit of storage and I/O.

Data Object

A set of extents that contain all the data blocks associated with the object; can be a file, file system, dataset, or database object.

Database Extent

A logical storage structure that holds a contiguous string of data blocks that are allocated by the database server for the management of a particular database file.

Database Instance

A set of database operating system processes, or threads, running on a host.

Database Partition

A manageable unit of a large database or object.

Database Schema

A collection of related database objects including tables, views, and other objects.

Database Segment

A set of extents that contain all the data blocks for a specific logical storage structure or object within a tablespace.

Database Table

A relational database structure that comprises vertical columns and horizontal rows of data.

Database Tablespace

A named storage area that physically allocates space for the database files.

Delta Sets

The predefined, timed cycles of collected data within an SRDF/Asynchronous session. Delta sets are used to transfer data efficiently by minimizing the redundancy of same track changes over the link between a source (R1) device and a remote target (R2) device.

Dependent Write

Consistency

A state that is achieved when all writes to a target (R2) device are consistent with data on the source (R1) device.

Destage

The asynchronous write from cache to disk device of new or updated data.

Device

An entity, physical or logical, on which data can be stored. In the EMC Symmetrix array, multiple devices (hyper-volumes) can be defined on a single, physical disk drive.

Device Address

The hexadecimal value that uniquely defines a physical I/O device on a channel path. A SCSI address consists of a Target ID and a Logical Unit Number (LUN).

Device Group

A user-defined name that specifies a group of associated devices, which support a common function, application, or database.

Differential Split

The splitting of a BCV pair that will only archive changed (differential) data from the first mirror to the remaining mirror set when the BCV split completes.

Director

An adapter (such as SA, EA, DA, DF, RA, RF) in the Symmetrix subsystem that acts as the interface between the host channels and disk devices during all control and data transfers.

Disk

An addressable part of the Symmetrix array that consists of a set of access arms, the associated disk surfaces, and the electronic circuitry required to locate, read, and write data.

Disk Group

A set of physical disks set aside to be used in creating devices of a particular protection level.

Domino Effect

An optional SRDF feature used to ensure that a remotely mirrored pair is always synchronized.

Dynamic RDF Group

RDF groups that are added on-the-fly (while the Symmetrix array is in operation).

Dynamic Reallocation

Volume (DRV)

A non-user-addressable Symmetrix device used by Symmetrix Optimizer to temporarily hold user data while reorganization of the devices is being executed. It is typically used by Symmetrix Optimizer during logical volume swapping operations.

Dynamic Spare

A Symmetrix feature that automatically transfers data from a failing non-mirrored disk device to an available spare disk device without affecting data availability.

E

Enginuity Consistency

Assist (ECA)

A TimeFinder feature that allows BCV devices to be split from their standard devices across multiple, heterogeneous hosts without the use of PowerPath.

Environment Variable        

Defines an aspect of the SYMAPI environment that can vary. Setting an environment variable changes the default environment and establishes a consistent rule for a specific component of the user's working environment for all affected calls that follow.

Establish

A business continuance process that assigns a BCV or RDF device as the next available mirror.

F

 

Failover

In an SRDF configuration, enables the target (R2) devices for read/write operations in the event that the source (R1) devices are unavailable.

G

 

Gatekeeper

A host accessible Symmetrix device, accessible by the host, through which SCSI commands executed by SYMAPI are routed to all Symmetrix devices.

Group Naming

Services (GNS)

An optional function of SYMAPI that provides the ability to store device and composite group definitions in a shared repository within each Symmetrix array. All GNS-enabled hosts across a Symmetrix environment will see the same group definitions, while sharing real-time updates to group definitions made by other hosts.

H

 

Hit Ratio

A percentage of I/O requests that resulted in cache hits (reads and writes serviced by cache).

Host Visible

A host connection to a specific entity exists in the current context. A device is host visible when a SCSI bus or Fibre connection exists and the Symmetrix configuration database has been updated to include that device (via a discovery operation).

Hyper-Volume

A storage area of a physical disk which was sectioned into 2 or more logical volumes (hyper-volumes). The host views hyper-volumes as individual physical devices. The number of possible hyper-volumes per disk depends on disk capacity.

I

Incremental Establish

A time-saving operation that copies from the source device to the standard device only new data updated on the source device while the pair was split.

Incremental Restore

A time-saving operation that copies from the source device to the standard device only new data updated on the source device while the pair was split.

I-Node

An internal file system data structure (for UNIX-based operating systems) that describes an individual file.

Invalid Tracks

The number of changed tracks on a device that are not synchronized between two or more mirrored devices forming a mirrored pair.

L

 

Local Device

A Symmetrix device that has a direct I/O channel connection to a host.

Logical Device Name

A name assigned to a device either at the command line or, automatically, when it is added to a device group (for example, DEV003 or BCV001).

Logical Unit Number

(LUN)

A unique number that identifies a specific logical unit; in the case of Symmetrix array it refers to storage devices. On a SCSI bus, it is a unique identifier that enables an array to differentiate devices for a given target (each of which is a logical unit). For Fibre Channel and iSCSI, it identifies a device address visible to the host HBA.

Logical Volume

Virtual devices that are made available to applications and databases.

M

Meta Device

A linked group of Symmetrix devices that can be acted upon as one target on the SCSI bus. A meta device consists of one meta head device and one or many member devices.

Mirrored Pair

A pair of locally or remotely established Symmetrix devices that are used to copy and synchronize data between the two devices for the purpose of creating an exact copy.

Mirroring

The replication of data on separate devices for the purpose of creating and identical copy. Each copy automatically updates during a write operation. If one disk device fails, the Symmetrix automatically uses one of the other copies from another disk drive.

Mount Point

A directory that can be associated with specified volumes in a persistent manner.

Multi-Hop

From the point of the managing host, a complex Symmetrix site configuration comprised of multiple (three or more) Symmetrix arrays that are linked together locally and remotely, which are used to manage and mirror data between devices in the arrays. Multi-hop configurations are limited to two hops (SRDF links) between

Symmetrix sites.

P

PermaCache

An area (slots) in Symmetrix cache memory that is reserved by a running SYMAPI storage process for preserving I/O throughput (defers the destaging of readily needed data). It improves program access speed to prioritized, but infrequently used data.

Physical Device

Name

The fully qualified path name or host name for a device (such as /dev/rdsk/c2t0d2s2). The physical device name can be referenced in a command or function argument, or shown in a display.

Physical Extents

A specified number of disk blocks; the smallest unit of disk space that can be assigned to a logical volume.

R

R1

See Source (R1) Device

R2

See Target (R2) Device.

RA Groups

The device groups in an SRDF environment. See RDF Groups.

RAID

Redundant Array of Independent Disks. Technology that allows a single set of data in different places on multiple hard disks, which improves performance and increases fault-tolerance.

RDBMS

Relational Database Management Systems. Software that creates and maintains a database system and the data stored in the system.

RDF Consistency

Group

See Consistency Group.

RDF Groups

Device groups (also known as RA groups) containing only RDF

devices that define communications paths between two separate

Symmetrix arrays. An RDF1 group type contains source (R1) devices and an RDF2 group type contains target (R2) devices.

RDF1/RDF2

The two types of RDF device groups containing RDF device pairs. See

RDF Groups.

REGULAR Device

A standard Symmetrix device type that is online and used for I/O operation from its host.

 

Restore

A business continuance process that reassigns a BCV device as the next available mirror of the standard device with which it was previously paired. The other standard device mirrors receive a full data copy from the BCV mirror.

S

SAVE Device

A predefined Symmetrix device (not mapped to the host) that provides the physical storage space used to store pre-update images or changed tracks during a virtual copy session. SAVE devices are configured into SAVE device pools for this purpose.

SAVE Device Pool

A container for SAVE devices that acts as a group for storing data in striped form.

SCSI Address

The hexadecimal value that uniquely defines a physical I/O device on a SCSI channel path. A SCSI address consists of a Target ID and a Logical Unit Number (LUN).

Semi-Synchronous

Mode

An SRDF mode of operation where applications are notified for each write once the data is in the cache of the local Symmetrix array. Writes are transferred to the target (R2) as the SRDF links become available. If source tracks are pending transfer to a target (R2) device, and a second write is attempted to the source (R1) device, the Symmetrix will disconnect (non-immediate retry request), and wait for the pending track to transfer to the remote Symmetrix array.

Single-Hop

From the point of the managing host, a Symmetrix site configuration comprised of two or more Symmetrix arrays linked together locally and remotely, which are used to manage and mirror data between the devices in the two arrays. Single-hop configurations are limited to one SRDF link between Symmetrix sites.

Source (R1) Device

A Symmetrix device that is participating in SRDF mirroring operations with a target (R2) device on a separate remote Symmetrix array. An R1 device must be assigned to an RDF1 group type (see RDF1/RDF2).

Split

A business continuance process that removes the BCV mirror from the existing BCV pair and assigns the BCV mirror back to its original device address. The BCV device then holds an instant copy of the data from the standard device.

SQL

Structured Query Language. The standardized relational database language for querying, manipulating, and updating information in a relational database.

SRDF

Symmetrix Remote Data Facility. An EMC business continuance solution that maintains a mirror image of data at the device level in Symmetrix arrays, which can be located at physically separate sites.

SRDF Link

The physical fiber optic connections and channels between the two Symmetrix arrays.

SRDF/A

An SRDF/Asynchronous mode of operation that provides a consistent point in time copy of data on the target (R2) device, which is a short period of time behind the source (R1) device.

SRDF/AR

An SRDF/Automated Replication business continuance solution that performs automated, consistent replication of data from standard devices via RDF1 BVC devices over SRDF links.

Standard Device

A Symmetrix device configured for normal Symmetrix operation under a desired protection method (such as RAID 1, RAID-S, RAID 5 and SRDF).

Storage Management

Initiative (SMI)

A SNIA initiative to develop a standard for storage management. The result of which is a standard management interface defined in a comprehensive specification (SMI-Specification or SMI-S). The SMI-S defines the open storage management interface that enables the interoperability of multiple vendor’s storage management technologies used to monitor and control storage resources in multi-vendor SAN topologies.

Striped Meta

A meta device in which each meta member device is divided into a set of stripes that cross all device members. When addressing a striped meta, data must be written (or read) across all devices (following the stripe) before advancing to the next stripe on the first device. When writing to a striped volume, equal size stripes of data from each participating drive are written alternately to each member of the set.

Symmetrix Device

Name

A Symmetrix-assigned hexadecimal number of a physical device.

Symmetrix ID

A unique 12-character Symmetrix ID assigned to each Symmetrix array (such as AB0010020064).

Symmetrix Integration

Utilities (SIU)

Disk management utilities used to setup and control a TimeFinder/Mirror or SRDF business continuance configuration for a Windows 2000 or Windows 2003 host. It provides the disk management functions missing from the Windows operating system when working with TimeFinder/Mirror and SRDF.

Symmetrix

Ordered-Write

Processing

An SRDF/A processing solution used to transfer host I/Os, that processes writes in groups as opposed to singularly. See Delta Sets.

Synchronous Mode

An SRDF mode of operation where applications are notified that an

I/O (or I/O chain) is complete when the remote Symmetrix array acknowledges that the data has been secured in its cache. Synchronous mode ensures 100% synchronized mirroring between two Symmetrix arrays.

Synchronous Mode

An SRDF mode of operation where applications are notified that an I/O (or I/O chain) is complete when the remote Symmetrix array acknowledges that the data has been secured in its cache. Synchronous mode ensures 100% synchronized mirroring between two Symmetrix arrays.

T

Target (R2) Device

A Symmetrix device that is participating in SRDF mirroring operations with a source (R1) device on a separate remote Symmetrix array. This device is not accessed by user applications during normal I/O operations. An R2 device must be assigned to an RDF2 group type. See RDF1/RDF2.

TimeFinder/Clone

A business continuance solution for creating point-in-time copies of a source device on multiple target devices. Once activated, the copy can be instantly accessed by a target’s host, even before the data is fully copied to the target device.

TimeFinder/Mirror

A business continuance solution for creating mirror images of standard Symmetrix volumes that can be non-disruptively split, and used as stand-alone point-in-time copies, while the standard volumes remain online for regular host operations.

TimeFinder/Snap

A business continuance solution for making pointer-based, space-saving copies of datasets or volumes on multiple target devices from a single source device. The copies are available to host immediately.

V

Virtual Device (VDEV)

Used with TimeFinder/Snap, a host-accessible device containing track-level location information (address pointers), which indicate where the copy session data is located in the physical storage.

Volume

A general term referring to a storage device. In the Symmetrix subsystem, a volume corresponds to single device visible to the host.

Volume Group

A designated set of physical devices.

Volume Shadow Copy

Service (VSS)

A volume that represents a duplicate of the original volume taken at the time the copy began.