Fibre Channel on an IBM storage server
IBM's Enterprise Storage Server (ESS) (code-named Shark) supports a number of protocols, including Fibre Channel, SCSI and FICON (IBM's Fibre-Channel-based replacement for ESCON connection to S/390 processors). In an open systems environment, it can be useful to mix attachments to make full use of the ESS' power. In that case you have to decide how many ports to devote to which kind of attachment.
The best answer, according to IBM is to set your port allotment according to the needs of your applications. Determining how much bandwidth each application will need can be tricky, but there are some rules of thumb you can apply. On is to use one Fibre Channel port for every 400 GB of storage used by the application, with a two-port minimum for redundancy. In general, IBM says, use eight Fibre Channel adapters (two in each of four host bays should handle just about any application). You can often get by with fewer adapters, for example for an OLTP application that doesn't need the ESS' sequential speed. In that case four adapters, one in each of four host bays should be enough.
IBM discusses this and other open-systems issues in a redbook titled "Implementing Fibre Channel Attachment On ESS", which is available at www.storage.ibm.com.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.