Best Practices for Mirroring
Before you create mirrors, plan out the high availability strategy.
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Standard mirrors protect against storage failure, not path (switch, storage server) failure. For full path protection, use AP, MPIO, or a Third Party AP option.
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Use dedicated mirror paths.
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For efficient use of disk space, both mirror volumes should be the same size.
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Balance the mirroring load. For example, if you need 100 mirrored volumes, consider defining 50 on Storage Server 1 with mirrors to Storage Server 2, and 50 on Storage Server 2 with mirrors to Storage Server 1.
IMPORTANT: Mirror path configurations, such as using specific mirror paths or redundant mirror paths, must be configured before creating a mirror. After a mirror configuration exists for a virtual volume, mirror path settings cannot be changed. Refer to Specifying the Mirror Path to configure before creating mirrors.
Multipathing Notes:
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For AP, verify that the Primary Storage Server is correct. The Primary Server is the Server that the application servers will communicate with first. From there, the Primary Server will mirror its data to the Secondary Server (the other server involved in the mirror).
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When using alternate path software, you need only map the virtual volume to the application server once. A second mapping will automatically be created to a second channel if one exists. Before applying, check the two application server mappings in the Virtual Volume Properties dialog and verify that these are the desired mappings.
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To successfully change from a standard to alternate pathing mirror, the primary volume must be available. If the primary volume has failed in the standard mirror, you cannot enable alternate pathing. You should perform a re-scan in Windows Disk Management on the application server ensure that the current status of all volumes displays.
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When using cluster path, you must map to two or more application servers.
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3rd Party alternate path works by alternating mappings to the primary and secondary volumes, always start by mapping the primary.
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When creating multiple mappings when using 3rd party alternate path, you must create the mappings one at a time and click OK between each mapping.
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When multi-mapping a virtual volume to one or more application servers, match all subsequent LUNs to the first LUN created when mapping. (If the matching LUN is not available, then the mapping will use the next available one.)