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Sinngle level Storage-Advantages

Hi,

I am new to this i-series world ,earlier i was involved with SAP on Windows platform,just started to be familiar with iseries.As i was reading through the various reference materials it was mentioned that iseries has single level storage concept which means each location, even in the auxiliary storage system is addressable,but i could not make what advantage it would provide as with it also data has to be paged in/out of RAM!!

Any Ideas.

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2 Answers

  • Jul 27, 2006 at 07:32 AM

    Hi,

    this is an excerpt from an iSeries overview, that is available at http://www.ibm.com/servers/enable/site/porting/iseries/overview/overview.html:

    "The benefit of providing a single, very very large address space, in which all objects on the system reside, is that applications need not tailor their memory usage to a specific machine configuration. In fact, OS/400, due to the single-level storage, does not need to tailor such things as the sizes of disk cache vs paging space. This greatly facilitates the on-demand allocation of memory among logical partitions."

    For example, when using the database with SAP, you don't need to define table spaces of buffers, but the System i memory management takes care of that automatically. Also, distributing data over new disk units that have been added recently, can be widely autmated (STRASPBAL).

    Kind regards, Christian Bartels.

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    Former Member
    Jul 28, 2006 at 02:14 AM

    Hi Tirtho,

    Welcome to the iSeries world!

    You may have got the basic idea about Single-level storage by now. It is an unique way of implementing Memory Management and File System on one of the earliest 64-bit Operating Systems. Christian has explained a few advantages of it.

    Regarding Page In/Out, it is inevitable that disks have to be used when memory requirement is bigger than the size of the physical memory. All implementations of virtual memory have to solve this issue one way or another - paging files on Windows, swap partition/files on Linux, and single level storage on iSeries. One advantage of addressing memory and hard drives (file system) in the same way (single level storage) is that it doesn't have to translate the virtual memory address to the physical position on the hard drives, which an auto-growing paging file cannot avoid and in turn have slower service speed when all other conditions are same. Hope you agree with it.

    Thank you,

    Victor

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