Free Trial

Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.

Share this Page URL
Help

Test results > Test results - Pg. 471

Each pair of bars indicates the activity rate and response time for the DASD supporting the file system containing the NAB. For instance, one can see from the chart that when running updall to rebuild views and indexes for the IBMUS NAB, the DASD had much less I/O activity (51.1 I/Os per sec. for HFS vs. 5.6 for zFS), and marginally better response time (9.9 msec for HFS vs. 8.8 msec for zFS). What is interesting is that for any given task, either the activity rate or the response time for the DASD associated with the zFS measurement may actually be higher than for zFS; however, in all cases, the overall I/O intensity (activity rate multiplied by response time) is better for zFS than for HFS. Table 12-8 Measurements for the offline housekeeping functions Function HFS I/O Intensity zFS I/O Intensity Difference HFS:zFS compact -c compact -b compact -B updall -RC create FTI 281 557 843 552 66 76 347 641 52 28 -73% -38% -24% -91% -58% 3.70:1 1.61:1 1.32:1 10.62:1 2.36:1 A closer look at the DASD response time reveals some details about how HFS and zFS perform their I/O to the physical device; see Figure 12-10. DASD Response Time for NAB HFS Compact -c z/FS Compact -c HFS Compact -b z/FS Compact -b HFS Compact -B z/FS Compact -B HFS Updall -RC z/FS Updall - RC HFS cfti z/FS cfti 0 2 4 6 8 10 12 Pending Disconnect Connect Total Response time (milliseconds) Figure 12-10 DASD response time for NAB There was no I/O service queue (IOSQ) time component to the response time for either the HFS or zFS measurements, which is to be expected, since there was only one thread of execution trying to use this file and its associated file system at a time. Several general patterns emerge from this chart: zFS has a slightly higher pending time in all cases, indicating longer waits in the path out to the device. This is likely due to a configuration reality of the environment, since the HFS, and zFS file systems were defined on different DASD devices, with different channel path characteristics. We don't believe this to be caused by zFS. In all cases except for the compact in place with file size reduction (compact -B), disconnect time for zFS is much better than for HFS. Disconnect indicates the amount of time that an I/O request is freed from the channel due to seek, latency, or rotational delays. Chapter 12. Tuning and performance 471