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Chapter 14. Monitoring z/VM and Linux 195

2 Paging to expanded storage is displayed here. Most z/VM systems on z9 class machines

can sustain several thousands of this type of paging operations a second without any

problems. The MIGRATE rate is the number of pages per second being moved from

expanded storage out to paging space on DASD. A healthy system will have a MIGRATE rate

significantly lower than the XSTORE rate, probably being measures in hundreds rather than

thousands. The higher values seen tend to build up over time, and are sustained over periods

of intense system activity; however, there are times when the MIGRATE value may spike for

brief periods of time.

3 Minidisk cache (MDC) statistics are displayed here. The effectiveness of MDC can be

judged by the combination of the READS rate and the HIT RATIO. If both are high, then a large

number of physical I/Os are avoided due to the MDC feature. For a system that has an

appreciably high I/O rate, composed of reads plus writes, and a high proportion of reads, and

a good hit ratio for those reads (tending to 90% or greater), the real, physical I/O avoidance

can be very high (as high as 50% in some cases has been observed). Conversely, however, a

high HIT RATIO with a low value for the READS rate should not be taken as desirable (a 100%

hit ratio, when doing only one I/O per second, is effectively meaningless).

4 More storage (memory) management is displayed here. The PAGING rate is important.

Higher values will often impact performance. This can be at least partially offset by increasing

the number of page volumes, but a more thorough examination of this problem is advisable

whenever it arises.The STEAL percentage is often misleading. This is basically the percentage

of pages taken from guests that z/VM believes are non-dormant. Because some guests have

periodic timers going off, they appear to be active to z/VM even when relatively idle. Pages

taken from these guests are still considered to be stolen. So there are scenarios where a

system only has a user set comprising active guests, in which case all pages taken would be

considered stolen. Bearing this in mind, if a high STEAL value is observed, the paging rate

needs to be checked. If the paging rate is relatively low, then the STEAL value is not important.

On lines

5 through 8, you also see a series of counters that represent the users in various

queues. The z/VM scheduler classifies work into three different classes (1 through 3), and a

special additional class labelled zero. So the Column of Qx values and Ex represent the

virtual machines in the dispatch list and the eligible list. The most important value here to

validate is that there are no virtual machines in the Eligible list: E1, E2, E3; this implies z/VM

has stopped dispatching some virtual machines to avoid over-committing resources. Such a

system would require further investigation, possibly leading to some tuning work, or even the

addition of some hardware in extreme cases. You can ignore the values in parenthesis.

INDICATE QUEUES EXP

Another useful command to help you determine the state of the system is INDICATE QUEUES EXP.

Following is an example:

==> ind q exp

DATAMGT1 Q3 AP 00000537/00000537 .... -2.025 A02

BITNER Q1 R00 00000785/00000796 .I.. -1.782 A00

EDLLNX4 Q3 PS 00007635/00007635 .... -1.121 A00

TCPIP Q0 R01 00004016/00003336 .I.. -.9324 A01

APCTEST1 Q2 IO 00003556/00003512 .I.. -.7847 A01

EDLWRK20 Q3 AP 00001495/00001462 .... -.6996 A01

EDL Q3 IO 00000918/00000902 .... -.2409 A01

EDLWRK11 Q3 AP 00002323/00002299 .... -.0183 A00

EDLWRK18 Q3 IO 00001052/00000388 .... -.0047 A00

EDLWRK4 Q3 AP 00004792/00002295 .... .0055 A01

EDLWRK8 Q3 AP 00004804/00004797 .... .0089 A02

EDLWRK16 Q3 AP 00002378/00002378 .... .0170 A02

EDLWRK2 Q3 AP 00005544/00002956 .... .0360 A00

EDLWRK12 Q3 AP 00004963/00002348 .... .0677 A01

1 2 ... 208 209 210 211 212 213 214 215 216 217 218 ... 267 268

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