Configuring PV Links

The examples in the previous sections describe the use of the vgimport and vgexport commands with the -soption. In addition, the mk1VGs script uses a -sin the vgexport command, and the mk2imports script uses a -sin the vgimport command. Optionally, remove this option from both commands if using PV links. The -soption to the vgexport command saves the volume group id (VGID) in the map file, but it does not preserve the order of PV links. To specify the exact order of PV links, do not use the -soption with vgexport, and in the vgimport command, enter the individual links in the desired order, as in the following example:

#vgimport -v-mmapfilename vgname linkname1 linkname2

Grouping the Symmetrix Devices at Each Data Center

The use of R1/R2 devices in M by N configurations of multiple Symmetrix frames is enabled by means of consistency groups. A consistency group is a set of Symmetrix RDF devices that are configured to act in unison to maintain the integrity of a database. Because Metrocluster with EMC SRDF works at the device group level, the consistency group is implemented and managed as a single device group even though it spans multiple Symmetrix frames. Consistency groups are created using either EMC PowerPath or RDF Enginuity Consistency Assist (RDF-ECA) feature of Solutions Enabler. In a consistency group, Symmetrix tracks the I/Os that are written to the devices. If an I/O cannot be written to a remote Symmetrix because a remote device or an RDF link has failed, the data flow to the other Symmetrix will be halted in less than one second. Once mirroring is resumed, any updates to the data is propagated with normal SRDF operation.

Figure 46 shows when there is a break in the links between two of the Symmetrix frames, the use of consistency groups (depicted as dashed oval lines) ensures that the other two links are also suspended.

Figure 46 2 X 2 Node and Data Center Configuration with Consistency Groups

Setting up M by N Configurations

Metropolitan clusters using EMC SRDF can be built in configurations that use more than two EMC Symmetrix disk arrays. In such configurations, M arrays located in Data Center A may be connected to N arrays located in Data Center B. This section describes how to set up an M by N configuration using EMC Solutions Enabler and HP-UX commands. It is assumed that either Symmetrix PowerPath software is installed or RDF-ECA feature of Solutions Enabler is enabled on all nodes and the

Building a Metrocluster Solution with EMC SRDF 265