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Managing Truly Flexible SAN Fabric Designs
The real power of zoning lies in its ability to be used in a combination of zone types. Hard zones, the most secure of all zoning, allow the fabric to be partitioned into multiple, independent, virtual fabrics. The entire fabric is transparently treated as a single hard zone if no hard zones are defined.
Other zones can be overlapped within hard zones, which allows some ports to be dedicated to private legacy devices using SLZs. For efficient SAN utilization and ease of management, all other ports can be zoned using the port and WWN name server zones to allow all devices to be connected. Finally, in order to limit the impact of IP broadcasts on SCSI devices, broadcast zones can be used if IP traffic is present. All zone types can be configured on fabrics of any size, with no limitations as to which ports or devices in a fabric can be placed into a zone for maximum ease in growing large fabrics.
Combination Zoning Examples
A few real-world examples of the benefits of creating sub-zones within a hard zone include:
- Allowing private loop devices to share the same switch with public devices. Both private and public devices will operate independently using the same switch, thus reducing the number of switches necessary to build the fabric.
- Dedicating an ISL from one switch to another within a zone.
- Dedicating known I/O bandwidth within a zone.
- Overlapping specific port or WWN groups dynamically on the fly for data backup and then reconfiguring the zones to their original configuration.
- Limiting IP broadcasts to specific devices in multiple zones within the hard zone, and overlap those broadcast ports with name server zone ports to communicate to other devices in the SAN.
- Segregating specific company departments.
The New Hierarchy In Zoning
A new hierarchy within a zone set is defined by the latest American National Standards Institute (ANSI) standards.
The highest level of the zoning hierarchy is a zone set. Assigned zones are contained in the zone set, and assigned members are contained in the zones. Thus, in a single fabric, there can be several zone sets; however, only one zone set can be active at any one time. For example, in order to perform backup when moving a tape library from one server to another, multiple zone sets are especially helpful for dynamic reconfiguration of the SANs.
The administrator simply deactivates the old zone set and activates the new in order to change zone sets. While this can be done without bringing down the SAN, when I/O activity is present in the SAN, it should not be performed. Instead, when the SAN is idle, active zone sets should be changed.
Now called "members," zones are made up of a group of assigned devices (similar to an original SAN switch). Additionally, within the zone set, all device members assigned in the zone can belong to one or multiple zones. With multiple storage devices, this capability helps facilitate the sharing of backup devices.
Within a zone, members are simply devices. With a SAN switch, member devices can be assigned to a zone via the port number, Fibre Channel Address (FCA), or the world wide name (WWN). So, within a SAN, any member can be assigned to multiple zones.