Tip

Finding a common language between mainframes and SAN

One reason mainframe and open systems staff without cross system experience don't communicate clearly is: language. Although both groups think they are speaking clearly, neither group actually understands the other. For reasons having to do with job security and industry FUD, vendors have used different terms to mean basically the same thing.

Mainframes and midrange systems can be divided into smaller logical system images. LPARs are logical partitions of the mainframe hardware. Each LPAR runs a separate copy of the operating system. Large RS/6000 systems can be physically subdivided into nodes. Each node runs a separate copy of the operating system.

While this provides a similar result, the logical versus physical distinction is very important, especially in terms of I/O. An LPAR can be defined to access any I/O device connected to the mainframe hardware. An RS/6000 node can only access I/O devices physically connected to that node.

Disk I/O connectivity for mainframes and RS/6000's is accomplished by connecting an internal adapter of some kind to an external physical device. (In making this comparison, I am ignoring the capability of both to have some internal devices.) Mainframes use an adapter called a channel. RS/6000 systems use a host bus adapter (HBA). Channels come in copper bus/tag, ESCON and FICON. HBAs can be copper SCSI or Fibre Channel (FC).

Mainframe FICON channels and RS/6000 fiber channel HBAs are both variations of the FC standard. At the

    Requires Free Membership to View

physical level and the lower protocol levels, both are identical. It is easy to think of a channel and an HBA being the same.

Where channels and HBAs differ is the amount of connectivity that a mainframe LPAR or an RS/6000 node can provide. A mainframe LPAR can have 100 or more FICON channels associated with it and share those channels with other LPARs. An RS/6000 node can have no more than two fiber channel HBAs installed in it and can not share these HBAs with other nodes.

Using an IBM Shark disk subsystem as an example, the mainframe LPAR can have sixteen FICON channels from one LPAR. A single RS/6000 node can have two FC HBA connections. Mainframe operating system software will automatically support I/O load balancing across the sixteen paths and handle fail over. The RS/6000 requires additional software drivers be installed to handle load balancing and fail over. These differences must be understood by the SAN designer.

Another area of confusion is switches. The only switches in a mainframe disk I/O environment are McData or Inrange enterprise class directors with all the high end availability features. In the RS/6000 world, switches can be either low/mid range switches such as the Brocade models or enterprise class directors. Since the word switch is used to describe both, it is important to define the actual type and model of switch.



About John Weinhoeft:

For the past 30-plus years John Weinhoeft has had his hand in the computer industry. He recently retired from designing and managing the State of Illinois' centralized computer systems that served 100 agencies. John has authored and edited a number of analytical books published by Computer Technology Research Corporation. He is, or has been, a member of several computer organizations including the Computer Measurement Group and Central Illinois Personal Computer Users Group.

Send John your comments

This was first published in March 2003

There are Comments. Add yours.

 
TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

Disclaimer: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.