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In the Version 5 Release 1 announcement made in April 2001, IBM announced two new hardware adapters which support Fibre Channel attachment - the #2765 Fibre Channel Tape Adapter and the #2766 Fibre Channel Disk Adapter. These new features offered improved connectivity to external storage devices, and I thought therefore that it would be worth using this month's article to discuss these and in particular the capabilities of the Disk Adapter.
Since these are hot-pluggable adapters they are supported only on the 8xx and 270 iSeries models, and not on earlier AS/400 models. They also both require Version 5 Release 1 as a prerequisite, and they are not supported by any earlier release of the operating system.
The #2766 Disk Adapter attaches IBM's Enterprise Storage Server (ESS), which is a San that can be used for external storage by the iSeries system. The AS/400 and iSeries already supported the attachment of ESS via a card called the #6501 Tape/Disk Controller. This was an SPD technology card first announced in 1993. It clearly therefore is not new technology as is shown by the fact that it offered SCSI attachment at a rate of 20 MB/sec. The #2766 supports 100 MB/sec full duplex operation and therefore will offer improved performance for attaching ESS to an iSeries system.
However, although the connectivity is improved with the #2766, there are other issues to be considered when proposing that an ESS be installed to support an iSeries system. A San can offer benefits by consolidating the storage infrastructure of multiple, heterogeneous platforms into a single set of centrally managed resources. For customers with multiple Unix and PC Servers - which could come from a number of different manufacturers - a San offers considerable benefit in variety of areas - improved storage management, backup and recovery, availability, capacity and performance. The iSeries can also benefit from the functionality that is offered by ESS. However, I would urge caution in adopting this solution, because there are certainly circumstances in which this is not the best approach so far as the iSeries is concerned.
Core line apps
The most important reason for this is because in the vast majority of cases customers are using their iSeries system for core line of business applications. These applications are generally critical to the running of the business and, as a result, a fast, predictable response time from the system is equally critical. With storage facilities provided by an external San which could also be supporting many other servers, it may be very hard to ensure such a fast, predictable response time. With its internal storage the iSeries already effectively offers its own San with many of the functions that in the case of Unix or PC Servers are offered only by using a San. And by using internal storage you can be sure that you have full control over the system's performance.
That is not to say that there is not a place for ESS connected to iSeries. For customers who have a range of heterogeneous servers including numbers of Unix and PC Servers, and who have perhaps only a relatively small iSeries installation which is not critical to the business; and who want to take advantage of the benefits that a San would give them, particularly for their Unix and PC Servers, then this may well be an attractive option. There will also be other situations where a San can be of benefit because of its flexibility in being able to support many different server platforms. For customers who are currently using ESS connected to the older #6501 controller then, if they are using an iSeries system, a move to the Fibre Channel Adapter for ESS attachment should give significantly improved performance. However, in most iSeries installations it will probably continue to be the case that it is best to use internal storage.
The #2765 Fibre Channel Tape Controller offers marginal performance improvement over the previously available SCSI attachment of tapes. The main benefits of Fibre Channel here are increased distance - allowing directly attached tape drives to be up to 500 metres away, or up to 10 km away if using hubs; and the sharing of tape devices - by connecting a tape drive to multiple iSeries servers via a switch.