Windows Knowledge Base

[DMX]Preparation Before Change

Before making configuration changes, you must thoroughly understand your Symmetrix configuration. The following guidelines help to establish safe disciplines as you begin any change that can easily impact stored data:

1. Verify that the current Symmetrix configuration is a viable configuration for host-initiated configuration changes.
To verify your current Symmetrix configuration is ready for changes, enter:

symconfigure verify -sid SymmID

2. Before creating new Symmetrix devices, check for free physical disk space using the following command:

symconfigure list -freespace [-units CYLINDERS|MB] -sid SymmID

Free disk space on unformatted disks is shown as available for all emulation modes. New Symmetrix devices will be created first on physical disks that have no prior allocations, causing these disks to be committed to that emulation type.
Examine the distribution of freespace across formatted disks to see if the desired mirroring can be provided using one of the following commands:

symdev list -sid SymmID -da all -space

or

symdisk list -sid SymmID

3. No configuration change is activated in the Symmetrix system until you commit the action.
Some classes of change operations may or may not impact current I/O. When possible, before you commit any action, stop I/O activity on the Symmetrix devices to be altered during a configuration change session. Consider the Impact on I/O statement for each class of operation in this chapter before working on any online devices.

If required, set the impacted device(s) for change to be Not Ready using the following command form:

symld -g DgName not_ready [LdevName [LdevName... ]]

Note: If I/O activity on an affected Symmetrix device occurs before or during a commit action, the commit action might fail. At the very least, heavy I/O activity on unaffected devices will impact how long it takes to commit changes.

4. Ensure that all your critical data is preserved and safe when creating new or changing device configurations. Do not store data on any device that is not mirrored, or RAID-protected.
All final configurations and device attribute adjustments must meet certain open systems guidelines detailed in the E-Lab™ Interoperability Navigator, which can be viewed at http://elabnavigator.EMC.com.
Contact the EMC Customer Support Center for assistance in reverting to your previous configuration should there be unforeseen problems with the new configuration.

5. After committing a symconfigure mapping operation, you must update the device mapping information within the host system environment. Attempting host activity with a device after it has been removed or altered, but before you have updated the host’s device information, can cause host errors.
To update your hosts, run the utilities specified for your platform as described in Appendix A, “Updating the Host.” The symcfg discover command should then be issued to update the SYMAPI database with the new device mapping information. After the host environment is updated, I/O activity can resume with the Symmetrix device.