Developers Guide

Server configuration
25 Dell EMC SC Series with Red Hat Enterprise Linux 7x | CML1071
3 Server configuration
This section discusses the various configuration aspects of the I/O stack of a Linux host. The Linux I/O stack
can be precisely configured to adapt to the needs of the environment in which the Linux host operates. The
configuration aspects include tuning the HBA port retry count, queue depth, SCSI and iSCSI device timeout
values, and more.
3.1 Fibre Channel and modprobe
The Linux modprobe facility provides a means to manage and configure the operating parameters of installed
FC HBAs (such as QLogic and Emulex). The modprobe facility is configured by editing or creating text files
within the /etc/modprobe.d directory.
3.1.1 Configuration
QLogic and Emulex HBAs are managed by configuration syntax that is written within individual text files,
located in the /etc/modprobe.d directory. Create these files if they do not already exist. The configuration
syntax for QLogic and Emulex hardware is discussed in detail in sections 0 and 3.8, respectively. If these files
do not exist in a fresh RHEL 7.x installation, they can be created manually using any text editor.
 For QLogic:
/etc/modprobe.d/qla2xxx.conf
 For Emulex:
/etc/modprobe.d/lpfc.conf
3.1.2 Reloading modprobe and mkinitrd
After configuration changes are made, reload the modprobe facility for the new or updated configurations to
take effect.
For local boot systems, it is recommended to unmount all SAN volumes and reload the module. The module
should be unloaded from memory before it is reloaded as follows.
# modprobe –r qla2xxx
# modprobe qla2xxx
Replace qla2xxx with lpfc if working with Emulex hardware; SAN volumes can be remounted subsequently.
For configuration persistence, the initramfs-*.img file needs to be rebuilt so that the new configurations are
incorporated during boot time. The following methods demonstrate rebuilding the initramfs-*.img file. This
process overwrites the same file in its existing location. It is recommended to back up the existing initramfs-
*.img file before applying this procedure. The two commands can be used as follows
# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.$(date
+%Y%m%d-%H%m)
# dracut --force
Ensure that the GRUB entry in /boot/grub2/grub.cfg points to the correct initramfs-*.img file and reboot the
system.