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Rev up the IFS with *TYPE2 directories

Site expert Tim Granatir says there's no reason not to use *TYPE2 directories. They significantly improve IFS performance, and they're more reliable than the *TYPE1 variety.

If you've used the IFS for any length of time, you've probably noticed that performance is sometimes lackluster. That became apparent to us a couple years ago when we decided to take an off-the-shelf application that was running on a Windows NT server and run it on the iSeries using the IFS in place of the NT server. Everything worked fine, but the first comment our employees had was that large database accesses took longer than when the application files were on the NT box.

Despite the sometimes less-than-stellar performance, security reasons prompted us to keep the application on the iSeries. So when IBM announced in V5R2 that it was revamping the directory structure of the IFS, we eagerly waited to see what it would do. What they gave us were *TYPE2 directories, which replace the old *TYPE1 directory implementation that has existed since the IFS was introduced.


Tim Granatir

After converting our directories to*TYPE2, I can't think of a single reason why anyone would NOT want to convert their directories to this new structure. Performance is much better (1.5 to 12 times faster, depending on what you are doing) and there is an increased reliability over the older *TYPE1 variety.

If you're like us, you may have multiple iSeries servers and you're worried about compatibility with your other machines if you convert some of them to the new type. Have no fear: Type 1 directories can be saved and restored to *TYPE2 directories AND vice versa. *TYPE2 directories are also capable of storing more links per directory (up to 1 million) where *TYPE1 was limited to 32,765. For iSeries Navigator users, objects will be sorted in name order when viewing objects in Type 2 directories.

To do the conversion, IBM has a command called CVTDIR. The only bad news, if you can even call it that, is that *TYPE2 directories are available only for the root, QOpenSys and user-defined file systems (UDFS). And once you convert a directory to *TYPE2, there is no utility to convert it back. Considering that *TYPE1 and *TYPE2 directories can peacefully coexist with each other, that isn't really a big deal, just something to be aware of. Depending on the number of objects per directory, your disk utilization could increase slightly by going to *TYPE2. But if your number of objects per directory is small, it should decrease.

The convert directory command can also provide you with conversion time estimates as well as pre-create some of the needed objects so that your actual conversion will go quicker. In our case, the conversion ran quicker than the estimated time and was uneventful.

I also found out after the fact that the Type 2 directories are available in V5R1 by applying certain PTFs. More information on that can be found here.

*TYPE2 directories are a further refinement and improvement in the IFS. With so many benefits, the only part I wonder about is why the conversion to *TYPE2 directories is optional at all.

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About the author: Tim is vice president of Technical Services at Interlink Technologies in Maumee, Ohio, where he serves as chief architect for their warehouse management system. He has worked in the banking, insurance, healthcare and distribution industries in various positions, including programmer/analyst, systems analyst and DP manager. Tim has worked on IBM midrange platforms since 1983.

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