Intel 7xx Servers, 170 Servers, AS/400 RISC Server manual 13.7 DB2 UDB for Linux on iSeries

yCost. Because the disk is virtual, it can be created to any size desired. For some kinds of Linux partitions, a single modern physical disk is overkill -- providing far more data than required. These requirements only increase if RAID, in particular, is specified. Here, the Network Storage object can be created to any desired size, which helps keep down the cost of the partition. For instance, for some kinds of middleware function, Linux can be deployed anywhere between 200 MB and 1 GB or so, assuming minimal user data. Physical disks are nowadays much larger than this and, often, much larger than the actual need, even when user/application data is added on.

ySimplification and Consolidation. The above advantages strongly support consolidation scenarios. By "right sizing" the required disk, multiple Linux partitions can be deployed on a single iSeries, using only the required amount of disk space, not some disk dictated or RAID-5 dictated minimum. Additional virtual disks can be readily added and they can be saved, copied. etc. using OS/400 facilities.

In terms of performance, the next comparison is compelling, but also limited. Virtual Disk can be much faster than single Native disks. In a really large and complex case, a Native Disk strategy would also have multiple disks, possibly managed by the various Linux facilities available for RAID and striping. Such a usage would be more competitive. But we anticipate that, for many uses of Linux, that level of complexity will be avoided. This makes our comparison fair in the sense that we are comparing what real customers will select between and solutions which, for the iSeries customer, have comparable complexity to deploy.

y1 disk Intel box, 667 MHz CPU: 5 MB/sec for block writes, 3.4 MB/sec for block reads.

yVirtual Disk, OS/400 1 600 MHz CPU: 112 MB/sec for block writes, 97 MB/sec for block reads

As noted, this is not an absolute comparison. Linux has some file system caching facilities that will moderate the difference in many cases. The absolute numbers are less important than the fact that there is an advantage. The point is: To be sure of this level of performance from the Intel side, more work has to be done, including getting the right hardware, BIOS, and Linux tools in place. Similar work would also have to be done using Native Disk on iSeries Linux. Whereas, the default iSeries Virtual Disk implementation has this kind of capability built-in.

13.7 DB2 UDB for Linux on iSeries

One exciting development has been the release of DB2 UDB V8.1 for Linux on iSeries. The iSeries now offers customers the choice of an enterprise level database in Linux as well as OS/400.

The choice of which operating environment to use (OS/400 or Linux) will typically be determined by which database a specific application supports. In some cases (e.g., home-grown applications), both operating environments are choices to support the new application. Is performance a reason to select Linux or OS/400 for DB2 UDB workloads?

Initial performance work suggests :

1.If an OLTP application runs well with either of these two data base products, there would not normally be enough performance difference to make the effort of porting from one to the other worthwhile. The OS/400-based DB2 product is a bit faster in our measurements, but not enough to make a compelling difference. Note also that all Linux DB2 performance work to date has used the iSeries virtual storage capabilities where the Linux storage is managed as objects within OS/400. The virtual storage option is

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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