The SRDF (Symmetrix Remote Data Facility) product family of EMC supports replication of data on a local storage system to one or more remote storage systems. For example, with concurrent SRDF data is simultaneously mirrored to two remote storage systems. This is also referred to as "remote copy" for short.
SRDF is offered in the same way for Symmetrix and VMAX3. The statements in this chapter therefore also apply for VMAX3.
SRDF links between VMAX3 and Symmetrix are also possible. The prerequisites are described in the EMC documentation.
The local and remote storage systems are linked to each other by at least two remote link directors (remote adapters, RAs; see figure 22 in "SRDF configurations"). Each storage system can be linked to several others by means of remote links.
Links via the RA can be implemented using Fibre Channel or GigE (Gigabit Ethernet).
With a Fibre Channel connection, two storage systems can be up to 10 km apart. Longer distances between two storage systems are possible if extensions are used. Regardless of the distance involved, SRDF can be used in unidirectional or bidirectional configurations.
If a storage system crashes, the current data (when synchronous SRDF processing mode is used) always also exists on the remote storage system. As far as data is concerned, this means that after a failure:
the current data does not have to be reimported,
no check is necessary to determine whether the backups are usable or consistent,
there is no need to roll back to an obsolete status.
In addition to synchronous replication using SRDF, SRDF/A also features asynchronous replication with cross-volume data consistency. This ensures that consistent, up-to-date data is available on the remote storage system after a failure.
Any application can use SRDF since it is operated by the storage system itself, regardless of the operating system version.
Remote copy pair (single SRDF configuration)
The remote copy pair consists of the source unit (original) and the target unit (data copy) that are connected to each other by means of a remote link.
The source unit is in the storage system that receives the writes in normal remote copy mode. It sends the updated data to the remote storage system, which saves the data on the target unit. The remote copy pair can be preconfigured statically or (only with VMAX3 or higher) set up dynamically, e.g. with the SHC-OSD command /START-REMOTE-COPY (dynamic remote copy pairs).
Concurrent remote copy pairs (concurrent SRDF configuration)
With concurrent remote copy, the source unit (original) has two target units connected via remote links. The source unit is in the storage system that receives the reads and writes in normal remote copy mode. It sends the updated data simultaneously to both remote storage systems, which save the data on the target units.
Concurrent remote copy can be configured using the SHC-OSD command /START-REMOTE-COPY.
For source units which are used as the original in concurrent remote copy replication, the SHOW-REMOTE-COPY command displays both mirror pairs in two lines.
Cascaded remote copy pairs (cascaded SRDF configuration)
With cascaded remote copy, the target unit (data copy) of a remote copy pair is simultaneously also the source unit (original) of a (cascaded) remote copy replication to another target unit which is connected via remote links.
Cascaded remote copy can be configured using the SHC-OSD command /START-REMOTE-COPY.
For units which are used simultaneously as a source unit and a target unit in cascaded remote copy replication, the SHOW-REMOTE-COPY command displays both mirror pairs in two lines.
For these volumes the /SHOW-SYMMETRIX-DEVICE-CONFIG command displays a “B” for “both” for remote copy usage.
Remote link director (remote adapter, RA)
The remote link director is a channel adapter for the FC connection or for GigE connections (Gigabit Ethernet). It is used to connect the local and remote storage systems for remote copying.
Each RA has one to four ports (VMAX3: up to 32 ports), each of which can be used for remote links. The RA has a logical status (ENABLE or DISABLE). The director is active only when the logical status is ENABLE and the status of the port (storage system control panel) is CONNECTED.
A remote copy pair has at least two RA ports that function as remote links between source and target units. The remote link for the pair is AVAILABLE when at least one of the two remote links is available. If the remote link is not in the AVAILABLE status, the source and target units are not synchronized.
An RA can serve several logical RA groups (e.g. for switched SRDF or SRDF/A).
Switched SRDF
Remote link directors for FC connections can also be connected to several remote storage systems via an FC switch. A configuration in which the remote link directors are connected via a SAN is referred to as a switched SRDF. You can display all remote storage systems served by a remote link director using /SHOW-SYMMETRIX-CONFIGURATION ..., INF=*REMOTE-LINK-DIRECTORS.
Refer to the Support Matrix of EMC for information on which FC switches are supported.
RA groups
RA groups define the logical SRDF link between two storage systems and are set up in advance by Service or dynamically during ongoing operation. They are assigned numbers from 1 through 250. An RA group contains volumes and two or more RA ports. Each volume used for SRDF can be assigned to one RA group only or, as a concurrent SRDF source unit, to two RA groups. You can display the assignment using /SHOW-REMOTE-COPY-STATUS (see "SHOW-REMOTE-COPY-STATUS Displays the status of remote copy pairs") or /SHOW-SYMMETRIX-CONFIGURATION (see "SHOW-SYMMETRIX-CONFIGURATION Displays the configuration (Symmetrix/VMAX3)").
For VMAX3, RA groups can currently be displayed, but not managed, with SHC-OSD.
Commands for SRDF (Symmetrix/VMAX3)
Command | Function |
Interrupts remote copy mode | |
Changes the processing mode and remote copy parameters | |
Resumes remote copy mode | |
Sets the access path to the data of a remote copy pair | |
Displays the status of remote copy pairs | |
Displays the configuration | |
Displays device configuration | |
Creates a remote copy pair | |
Cancels a remote copy pair | |
Swaps the source and target property of a remote copy pair | |
Lifts locks | |
Lifts device locks |
SRDF functionality can be controlled for Symmetrix/VMAX3 using SHC-OSD. The SHOW commands display the status of the remote copy pairs, the SRDF settings and the configuration.