DB2 10 for Linux on System z Using z/VM v6.2, Single System Image Clusters and Live Guest Relocation

Chapter 5. Time synchronization 41

Using XEDIT, follow these steps:

1. Locate Features in the Features Statement section:

locate Features

2. Locate Enable:

locate Enable

3. Add three lines after Enable:

add 3

4. Fill with:

STP_TZ ,

STP_timestamping ,

STP_Timezone ,

5. Save the file:

file

6. If you are prepared to shut down and re-ipl the system, issue:

Issue: shutdown reipl

During the boot process Linux starts its own software-managed clock off of the hardware

clock. Alternatively, the clock can be set through operator commands. After the boot, the

Linux clock runs independently of the hardware clock. Because Linux manages its own

software clock, it frequently uses NTP (see 5.2, “Network Time Protocol (NTP)” on page 52)

to keep its time synchronized to an external source. If the Linux image (logical partition or

guest) has a Local Area Network (LAN) connection to an NTP server, Linux can take

advantage of it.

5.1.2 Relocating DB2 when using the hardware clock

Two tests were done using the hardware clock. In the first test, different timezone

configurations were set up on each of the two CPCs, while in the second test the CPC time

was manually changed. Linux and DB2 behavior were analyzed on both.

Test 1: Changing timezone configuration

The first test checks how Linux, and consequently DB2, handles relocation between two

CPCs in different timezones. ITSOSSI1 (z10™) is using the Central Standard Time (CST)

and ITSOSSI3 (z196) is using Eastern Daylight Time (EDT); check Figure 5-1 on page 42.

Note: STP_timestamping tells CP to enable the STP protocol (if the STP facility is

installed) and apply timestamps to all XRC-capable DASD devices.

STP_timezone, or STP_tz, tells CP to enable the STP protocol (if the STP facility is Issue:

shutdown reipl).

42 DB2 10 for Linux on System z Using z/VM v6.2, SSI Clusters and LGR

Figure 5-1 CPCs with different timezone configurations

Make sure the vmcp module is loaded so we can see on which VM system the server is

located by issuing the command shown in Example 5-3.

Example 5-3 Loading vmcp module

# modprobe vmcp

First we have the server set to use the hardware clock. Therefore, the Network Time Protocol

(NTP) daemon is not started. NTP is covered in the next section. At this point you simply

notice that it is not running during our first test (Example 5-4).

Example 5-4 Checking NTP daemon

itsolnx1:~ # /etc/init.d/ntp status

Checking for network time protocol daemon (NTPD): unused

The Linux guest is on the z/VM member ITSOSSI3 and has the CST timezone;

Example 5-5.

Example 5-5 Checking time settings on Linux and z/VM ITSOSSI3

itsolnx1:~ # vmcp q userid; vmcp q time; date

ITSOLNX1 AT ITSOSSI3

TIME IS 13:45:57 CST MONDAY 06/11/12

CONNECT= 00:01:34 VIRTCPU= 000:04.45 TOTCPU= 000:04.68

Mon Jun 11 13:45:57 CST 2012

In Example 5-6, ITSOSSI1 is set to a different timezone, EST (1 hour behind).

Example 5-6 Checking time settings on ITSOSS1

q time

TIME IS 12:45:57 EST MONDAY 06/11/12

SSI domain

z196

z/VM ITSOSS3

itsolnx1

LINUX

DB2 v10

Time: 12:45:57 CST

z10

z/VMITSOSS3

z/VM ITSOSS1

Time: 13:45:57 EDT

Relocation