Question: more CHPIDS to the same underlying physcial disks or to different disks?
Adding more CHPIDs provides more serving entities for I/O requests, but if all the I/O requests end up going to exactly the same physical drive, you haven't really done anything. Now, if the drive in question is behind a controller with lots of controller cache, the additional CHPIDs will provide an increase in the number of datapaths. Are all the CHPIDS on line and active? Is VM properly aware of them? Has VM disabled any of the CHPIDS? Is the I/O intensive App currently active and issuing I/Os are did it take a header when you added the CHPIDS? Is the real problem behind the I/O bottleneck caused by not spreading the logical/virtual disk over enough real disks? -----Original Message----- From: Wilson, Eric [mailto:[EMAIL PROTECTED] Sent: Thursday, August 28, 2003 10:50 AM To: [EMAIL PROTECTED] Subject: funky I/O change after adding CHPIDs All; Let me appoligize in advance; I'm a UNIX / Linux Admin, so I may not have the big iron terminology correct. Can anyone help us understand an interesting, yet seemingly bizarre and unexpected change in I/O throughput? Any insight in the Mainframe's I/O subsystem interaction with Linux would be greatly appreciated. We have RH v 7.2 running in 3 instances, on a z/800. We have an I/O intensive application seemed to bottleneck at the disk I/O level. To tune the I/O for greater throughput we more than doubled the number CHPIDs from 2 CHIPDs to 5 CHPIDs for VM. As illustrated in the sar output, in almost all measures, I/O seemingly decreased, rather than the expected increase. 08:20:02 AM tps rtps wtps bread/s bwrtn/s .... 10:00:02 AM 1631.95 1152.46 479.49 49424.93 4546.82 10:10:04 AM 1432.91 989.88 443.04 57652.88 3751.61 10:20:03 AM 1594.48 1096.06 498.43 63872.01 4187.39 10:30:02 AM 1561.13 1062.55 498.58 60807.45 4180.14 10:40:04 AM 1591.40 1073.45 517.95 61082.71 4326.86 10:50:02 AM 1546.10 1036.86 509.24 58992.35 4236.89 11:00:04 AM 1542.87 1035.01 507.87 57994.82 4222.20 11:10:03 AM 1523.59 1018.91 504.69 57183.95 4192.64 11:20:08 AM 1585.66 1061.96 523.69 59102.92 4347.70 .... point of CHPID additions ... 11:30:05 AM 289.59 206.67 82.92 10880.54 687.82 11:40:04 AM 320.85 221.71 99.14 11700.20 820.24 11:50:04 AM 323.05 228.10 94.95 11993.89 785.64 12:00:04 PM 350.41 243.22 107.19 13159.21 886.15 12:10:03 PM 244.28 168.34 75.93 9027.88 629.93 12:20:06 PM 354.44 245.26 109.17 13269.73 904.56 12:30:07 PM 318.21 226.82 91.38 11923.86 758.45 12:40:03 PM 330.88 227.47 103.40 12165.62 855.86 12:50:04 PM 322.11 231.72 90.39 12278.75 750.53 01:00:04 PM 335.75 231.46 104.29 12379.37 861.43 Cheers; E! ----------------- Eric Wilson IBM Certified Advanced Technical Expert RedHat Certified Engineer .~. /V\ /( )\ ^^-^^ Confidentiality Warning: This e-mail contains information intended only for the use of the individual or entity named above. If the reader of this e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, any dissemination, publication or copying of this e-mail is strictly prohibited. The sender does not accept any responsibility for any loss, disruption or damage to your data or computer system that may occur while using data contained in, or transmitted with, this e-mail. If you have received this e-mail in error, please immediately notify us by return e-mail. Thank you.
