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Symmetrix DMX & VMAX Devices Description

Symmetrix DMX & VMAX Devices Description


Symmetrix Devices are the LUN created on physical hard disks which present to Host or Symmetrix array internal usage. There are various types of devices in Symmetrix DMX & VMAX array. This document indicates the description of various types of Symm Devices for open system. The devices described in this document are categorized into five functional parts. They are Regular Device, Data Replication Devices, Virtual Devices, Device Pool Devices and System Devices.

Detailed Information

Regular Device:

Standard Devices:Standard volumes (STD) are configured for normal production operations. STD Devices are presented through SAN to Host for block level data R/W operation. There is no device type of Standard, but if a Symmetrix device is not one of any of the other Symmetrix Device types then it is considered to be a Standard device.

MetaDevice allows individual devices to be concatenated to create larger devices. The devices assigned in a meta sequence do not need to be adjacent. The metahead is the first device in the metadevice and is responsible for receiving incoming commands. When an incoming command for the metahead is processed, the Enginuity software determines which metadevice member should execute the command. Addressing of data contained in a metadevice can be organized in two different ways: 1. Concatenated devices: Concatenated devices are volume sets that are organized with the first byte of data at the beginning of the first device. 2. Striped devices: Metadevice addressing by striping divides each metamember device into a series of stripes, addressing a stripe from each device before advancing to the next stripe on the first device

Data Replications Devices:

BCV Devices: Business Continuance Volumes (BCV) is configured for TimeFinder/Mirror replication.

R1 and R2 Devices are configured for remote replication (SRDF is Symmetrix Remote Data Facility). An SRDF device group is a user-defined device group comprised of SRDF devices from a single Symmetrix array. At the time of creation, a device group must be defined as type REGULAR, RDF1, RDF2, RDF21, or ANY, and may contain various device lists for standard, BCV, virtual (VDEV), and remote devices. If the group type is defined as RDF1, RDF2, or RDF21, the group is considered an SRDF device group.

Possible dual-mirrored device types include the following:

R11: A concurrent R1 device with 2 R1 SRDF mirrors.

R21:  An SRDF device with 2 SRDF mirrors. One an R2 mirror and the other an R1 mirror.

R22: A concurrent R2 device with 2 R2 SRDF mirrors.

Diskless Devices (DLDEV): Diskless devices are used for cascaded R21s. They are cache only devices and do not consume disk space.

Virtual Devices:

Virtual Device (VDEV):Symmetrix virtual devices are configured as full-size devices, but use minimal disk storage on the back-end. On Symmetrix DMX & VMAX arrays, VDEVs reside in cache only and are depicted as having no back-end hypers. The format must be FBA. Virtual devices can also be used to form a VDEV metadevice. Other Symmetrix devices cannot be converted to form virtual devices. To configure a virtual device, set config=vdev in the device file.

Thin devices (TDEV) are devices that may or may not have storage allocated to them when they are created. To a host operating system, they look like regular devices with their configured capacity. The host treats them as regular devices and writes and reads from these devices like regular devices. Thin devices are bound to a thin pool (of DATA devices).

Device Pool Devices:

Following devices are contained in storage pool using virtualization technology. There are three types of device pools, Snap pools (contain SAVE Device), SRDF/A DSE pools, and thin pools (contain DATA Device)

SAVE Device: The device will become part of a pool of devices that are used with TimeFinder/Snap for virtual device Snap operations and SRDF/A DSE pool to extend the available cache space for SRDF/A sessions. Symmetrix SAVE devices work in conjunction with virtual devices and can be unprotected. To configure a SAVE device, set attribute=savedev in the request to create a new device.

DATA Device: The device will become part of a pool of devices that are used with thin devices for virtual operations. The Data Devices are grouped together into a storage pool called a Thin Pool. A Thin Device must be bound to a Thin Pool before it can be used. This Thin Pool provides the shared storage. The storage capacity in the Thin Pool can be shared among multiple hosts and applications

SAVE devices and DATA devices are created following the same procedure as for standard protected devices, with the additional specification of attribute=savedev or attribute=datadev.

System Devices:

There are some devices which cannot be categorized to above four parts. They are only for Symmetrix internal usage like configuration or data swapping:

DRV Device: Dynamic Reallocation Volumes (DRV) devices are configured Symmetrix Optimizer and FAST (Fully Automated Storage Tiering)

Gate Keeper Device (GK): Gatekeeper are used for special communication that controls Symmetrix array, like retrieving status, executing tasks.

Author: Fenglin Li



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