AIX Ver. 4 SysAdmin IV:Storage Management (Unit 10) – HAGEO and GeoRM

HAGEO – High Availability Geographic
GeoRM – Geographic Remote Mirroring

Unit Objectives
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Explain the risks covered by “classic” HA
Understand the various options for disaster recovery
Understand the components that make up HAGEO
Understand the structure of typical HAGEO clusters
Explain the functions of GeoRM

Classic High Availability
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Protection for typical risks (single points of failure) in a computer center
Automation of processes in the event of a fault

Disaster Recovery
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Protection from failure of an entire location (site failure)
Manual intervention may be necessary with client systems, routers, and so forth

Options in Disaster Planning
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Method Loss of data Downtime
Data backup to remote “Cold Site” appr. 24h > 24h
Data backup to remote “Hot Site” appr. 24h appr. 24 h
Electronic data replication Minutes < 24 h Complete site takeover Seconds < 1 h As above, but with two-phase commit none < 1 h Definitions - Cold Site - Backup equiment only - no operational hosts, etc. (requires the use of a mobile computer center for example) - Hot Site - Backup equipment and operational hosts What IS HAGEO? --------------------------- High Availability Geographic Extending HACMP to cover geographically separate sites - The cluster is organized into two sites: Special HACMP NIMs monitor geographic networks Dial back fail safe helps detect site isolation - Geographic Mirroring Devices replicate LVs between sites GMDs appear as logial volumes (any content). Kernel RPC service permits secure load-balanced transmission Synchronous and asynchronous (limited inconsistency) operation Failover both local and between sites - Setup of cascading resource groups "as usual" - Site failover (switching GMDs, and so forth) using pre-and post-events - Concurrent Access supported The Components of HAGEO --------------------------------------------- GeoMessage - Kernel extension and daemon process (rpc.geod) - UDP-based RPC service - Uses any number of IP based networks GeoMirror - Software device driver for the geographic mirroring devices - Uses GeoMessage and LVM - Carries out data replication and resynchronization where applicable GeoManager - Defined pre- and post-events (not a daemon process) - Implements the concept of the site - Controls DBFS and resource (re-)takeover Modes of Geographic Mirroring ----------------------------------------------- Each GMD can work in one of three modes 1. Synchronous - Data is written to the remote site first, then the local site - Application does not receive a return until data has been written to both sites - Very reliable, but at the expense of performance 2. Synchronous & Mirror Write Consistency - Data is written to local and remote site in parallel - State map is used to track progress of write operations to remote site - State map is cleared when local and remote write are completed - Application does not receive a return until data has been written at both sites - Extremely reliable, but at the expense of performance 3. Asynchronous - Data is written to local site and dispatched to remote site in parallel - State map is used to track progress of write operations to remote site - Outbound queue of write operations held on dispatching node. - State map is cleared when local and remote write are completed - Application receives a return when local write is completed - Good performance, but at the expense of relibility during failure Note: There were other slides that I did not enter for this unit.

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