Question/Comments from a searchStorage subscriber: This is regarding the "Performance and compatibility concerns" question.

It is a good idea to remember that the IBM Shark was designed as centralized storage solutions and you can mix both Mainframe and Open Systems platforms on the same box. The cache is very good when you mix both platforms.

The best thing is that Shark (as EMC Symmetrix) has a good technology to use point-in-time copy, remote copy (PPRC) and another good thing... you can use the same technology for both Mainframe and Open Systems with the same DASD.

The only problem with Shark is the compatibility with NT. I'm still hearing about the problems between Shark and NT environments.

If you want my personal opinion, the best DASD to mix platform (MF and OS) is EMC Symmetrix. I have a lot of Symmetrix installed mixing mainframes and open systems (Unix and NT) on the same Symmetrix, using TimeFinder and SRDF (remote copy) for both environments.


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Answer from Christopher Poelker: The issue of sharing storage with NT and Mainframe is one of resource contention. The Shark platform works fine in that environment until users start connecting many NT systems with the Mainframe. The same is true on the Symmetrix platform. Bus based and internal clustered architectures share bandwidth to the disk subsystems and cache. Contention for resources can occur (especially in cache) when multiple systems, using applications that have different requirements, try to contend with those resources. Unless the caching algorithm supports caching on a per LUN basis, one application performing sequential reads of large files (data mining for instance) will impact an application performing high random R/W I/O, as the cache requirements are quite different in those environments. Exacerbating this issue further is the fact that some vendors use part of their cache for metadata and firmware, and others use slower system memory as the cache itself.

This can be verified by running an OLAP and OLTP application on the same platform. Start the OLAP application and record performance statistics, then turn on the OLTP application and see the results (use high performance servers for this test).

The Shark box does have technology for Mainframe that greatly enhances performance (PAV) that some of the other vendors do not have. Symmetrix has proven software for remote copy and backup and, that does give them an edge in that area.

I always strive to be platform neutral in my responses here and do not like to point out weaknesses in particular vendors' platforms. I will try to continue to do so in the future.


This was first published in May 2001

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