Linux operation system setup

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The virtual machine resource definitions for the Cognos® BI and DayTrader servers are outlined in detail in topic Hardware and software configurations. Besides that, additional operating system tuning and setup changes were applied as described in this topic.

Networking

The Cognos BI Server components communicate over a virtual guest-to-guest network using a z/VM® Virtual Switch (VSWITCH). The virtual network devices appear as GuestLAN QDIO type in Linux™ when the network devices are listed with the lsqeth command.

Sample command: lsqeth for a virtual network device

# lsqeth eth1 
Device name                  : eth1                
--------------------------------------------- 
        card_type            : GuestLAN QDIO 
        cdev0                : 0.0.1000 
        cdev1                : 0.0.1001 
        cdev2                : 0.0.1002 
        chpid                : 02 
        online               : 1 
        portname             : osaport 
        portno               : 0 
        route4               : no 
        route6               : no 
        checksumming         : sw checksumming 
        state                : UP (LAN ONLINE) 
        priority_queueing    : always queue 2 
        fake_broadcast       : 0 
        buffer_count         : 128
        layer2               : 0 
        large_send           : no 
        isolation            : none 
        sniffer              : 0

The buffer count for the network devices was increased for all virtual machines:

Increased the number of buffers for inbound traffic to 128 (default is 64) at /etc/udev/rules.d/51-qeth-0.0.1000.rules
where 1000 is first cdev of the virtual network device in this case.
The following line was added to the udev rule definition to enhance the buffer count:
```
ACTION=="add", SUBSYSTEM=="ccwgroup", KERNEL=="0.0.1000", ATTR{buffer_count}="128"
```
See also Linux on System z® - Tuning hints & tips:
https://www.ibm.com/docs/en/linux-on-systems?topic=2018-tuning-hints-tips

Disk I/O on ECKD™ DASD

The I/O throughput for an ECKD DASD disk can be improved by using Parallel Access Volumes (PAV) or HyperPAV. This feature can be important for DASDs used with the Cognos BI Content Manager and Content Store where more disk I/O is expected.

The Linux DASD device driver can use this IBM® System Storage® feature to perform multiple concurrent data transfer operations to or from the same DASD instead of single data transfers. To use HyperPAV, there must be base and alias devices available, which require System z Input/Output Configurations Data Set (IOCDS) definitions. For HyperPAV on an IBM System Storage subsystem, the alias devices are not exclusively referenced to a certain base device, but they are eligible for all base devices in the same logical control unit (LCU). Linux handles HyperPAV alias devices in the same way as normal DASD base devices by using the chccwdev command or defining the appropriate udev rules for them. When listing the DASD devices with the lsdasd command, HyperPAV aliases can be identified by the alias status tag. The usage of the HyperPAV aliases is completely handled by the Linux kernel and is not noticeable by the users.

The sample command lsdasd shows four DASD devices and 20 HyperPAV aliases for the Content Store database server:

# lsdasd 
Bus-ID     Status      Name      Device  Type  BlkSz  Size      Blocks 
============================================================================== 
0.0.6980   alias                         ECKD 
0.0.6981   alias                         ECKD 
0.0.6982   alias                         ECKD 
0.0.6983   alias                         ECKD 
0.0.6e80   alias                         ECKD 
0.0.6e81   alias                         ECKD 
0.0.6e82   alias                         ECKD 
0.0.6e83   alias                         ECKD 
0.0.6e84   alias                         ECKD 
0.0.6e85   alias                         ECKD 
0.0.6e86   alias                         ECKD 
0.0.6e87   alias                         ECKD 
0.0.6f80   alias                         ECKD 
0.0.6f81   alias                         ECKD 
0.0.6f82   alias                         ECKD 
0.0.6f83   alias                         ECKD 
0.0.6f84   alias                         ECKD 
0.0.6f85   alias                         ECKD 
0.0.6f86   alias                         ECKD 
0.0.6f87   alias                         ECKD 
0.0.6926   active      dasda     94:0    ECKD  4096   21129MB   5409180 
0.0.6e01   active      dasdb     94:4    ECKD  4096   184688MB  47280240 
0.0.6e07   active      dasdc     94:8    ECKD  4096   100170MB  25643520 
0.0.6f07   active      dasdd     94:12   ECKD  4096   100170MB  25643520

For details about IOCDS configurations, see the Input/Output Configuration Program User's Guide, SB10-7037-11 at the Resource Link® (with a required registration):

http://www.ibm.com/servers/resourcelink

A detailed study addressing HyperPAV and databases can be found in the IBM white paper:

Oracle Database on Linux on System z - Disk I/O Connectivity Study

Other Linux operating system adaptions

For the Cognos BI Server Linux guests, especially the components that run under control of a WebSphere® Application Server, an increased limit for open files and number of processes was set.

Content of /etc/security/limits.conf: setting limits for number of open files and processes

# cat /etc/security/limits.conf 
# /etc/security/limits.conf 
# 
#Each line describes a limit for a user in the form: 
# 
#<domain>       <type>  <item>          <value>
…

*               -       nofile          65512 
*               soft    nproc           32768 
*               hard    nproc           32768

The limits can be permanently set in the Linux configuration file /etc/security/limits.conf.

By using the ulimit command, the values can be changed in a running Linux system. For example, you can set the number of open files:

ulimit  -n 16384