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

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

Last committed transaction = 2012-06-14-14.42.48.000000 UTC

DB20000I The ROLLFORWARD command completed successfully.

As expected, all records were restored (Example 5-25).

Example 5-25 All records have been restored sucessfuly even with the wrong timestamp

db2inst1@itsolnx1:~> db2 "select received,source from in_tray2"

RECEIVED SOURCE

-------------------------- --------

2012-06-14-10.41.37.626076 right1

2012-06-14-10.41.37.646395 right2

2012-06-14-10.42.48.478041 right11

2012-06-14-10.42.48.500735 right12

2012-06-14-10.27.58.757020 wrong1

2012-06-14-10.27.58.784167 wrong2

2012-06-14-10.30.37.366638 wrong11

2012-06-14-10.30.37.394163 wrong12

8 record(s) selected.

Results

As a result of the sequence of events in this case (Example 5-21 and Example 5-25), DB2

restore and rollforward commands are not affected by a configuration using the wrong time.

However, the data integrity is affected. Be aware that if your data uses a current timestamp, it

picks up the time from the guest and applications may face issues. Avoiding this issue is

analyzed in the next section.

5.2 Network Time Protocol (NTP)

A standard way of keeping dates synchronized is by using NTP. It is widely used to

synchronize computer clocks via the Internet. It will always keep the time synchronized in

your environment, even if it has been relocated to hardware that has the wrong time and the

server has been rebooted.

5.2.1 Configuring NTP

The NTP configuration file is located at /etc/ntp.conf. If you do not have this file, the NTP

package is probably not installed, so you can use the package management tool of your Linux

distribution to install it.

A basic configuration file follows in Example 5-26.

Example 5-26 ntp.conf basic configuration

# --- GENERAL CONFIGURATION ---

server aaa.bbb.ccc.ddd

# Drift file.

driftfile /var/lib/ntp/drift/ntp.drift

Chapter 5. Time synchronization 53

This basic configuration defines the server used to synchronize your time and a drift file that

stores the error frequency (drift). If the daemon is stopped and restarted it can reinitialize

itself to the previous estimate without spending time recomputing the frequency estimate,

based on the drift file. This file is required, so please check its permissions to avoid errors.

The file used in our lab had more parameters. This is just an example of the configuration

used in our experiments (Example 5-27).

Example 5-27 Configuration file used in our test server

itsolnx1:~ # cat /etc/ntp.conf

## NTP config file

# path for drift file

driftfile /var/lib/ntp/drift/ntp.drift

# alternate log file

logfile /var/log/ntp

#

# Authentication stuff

#

# path for keys file

keys /etc/ntp.keys

# define trusted keys

trustedkey 1

requestkey 1

server 9.56.248.20 iburst

restrict 9.56.248.20

This configuration uses some security parameters to control access to the NTP server. When

an NTP daemon is first set up, it is also set as an NTP server, not only as a

client, meaning that by default the NTP server is accessible from all hosts in your network.

The restrict parameter allows you to limit this access, if needed, and also will limit how the

NTP server acts on your server. In the configuration shown in Example 5-27,

we have not restricted access in any way, but for further information you can check the

ntp.conf man page or:

http://www.ntp.org/documentation.html

As soon as the configuration is complete, you can start the NTP daemon in order to start time

synchronization (Example 5-28).

Example 5-28 Starting the NTP daemon

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

Starting network time protocol daemon (NTPD)

done

Also, set NTPservice to load at boot time, which on SLES or Red Hat Enterprise Linux can be

done by using the chkconfig utility (Example 5-29).

Example 5-29 Setting up NTP to start at boot time

itsolnx1:~ # chkconfig ntp on

itsolnx1:~ # chkconfig --list ntp

ntp 0:off 1:off 2:off 3:on 4:off 5:on 6:off