udev config for RAC systems at Linux

We are using RHEV in our environment
- At first, assign shareable disks to both RAC servers in RHEV
  ( make partition at disk. Use vdc1 instead of vdc. It automatically correct alignment problem etc. )
- Disks must be assigned with VirtIO-SCSI instead of VirtIO
- udev rules must be written with disk serial numbers or with globally unique UUID numbers.
- afterwards udev will create regarding ASM devices for RAC

VirtIO-SCSI has many benefits over VirtIO ( unlimited PCI device, SCSI persistent reservation etc. )
Also for udev to work efficiently, we will write udev rules regarding serial number and WWN, but with VirtIO those values are not healthy.
For details about Linux VirtIO disk serial number problem, please refer to "linux-virtIO-udev-problem.txt"
Also you can examine this redhat article ==> https://access.redhat.com/solutions/500943
** because of this, you may also prefer UUID values.

For all best practices for RAC in Linux please examine below wonderful redhat articles.
 https://access.redhat.com/articles/1357883                   *****
 https://access.redhat.com/sites/default/files/attachments/deploying_oracle_rac_12c_rhel7_v1.2_updated_08-01-2016.pdf

                                    Feel free to communicate by bulent.yucesoy@gmail.com


##### DISK SERIAL WAY

- query disk serial

[server01]/#udevadm info --query=all /dev/vdc1 | grep ID_SERIAL | cut -d "=" -f2
a4c1259b-8093-464c-b
[server01]/#

- create udev rules file.

[server01]/etc/udev/rules.d#head -1 99-oracle-asm.rules
ACTION=="add|change", ENV{ID_SERIAL}=="a4c1259b-8093-464c-b", SYMLINK+="ASM_DATA_1", OWNER="oracle", GROUP="oinstall", MODE="0660"
[server01]/etc/udev/rules.d#

##### UUID WAY

--- get UUID

[server1]~#dmsetup ls | tail -1
mpathf1  (253:8)
[server1]~#dmsetup info mpathf1
Name:              mpathf1
State:             ACTIVE
Read Ahead:        8192
Tables present:    LIVE
Open count:        1
Event number:      0
Major, minor:      253, 8
Number of targets: 1
UUID: mpath-3600a098038304635502b4d416652654a
[server1]~#


-- create udev rules file.

[server1]~#head -1 /etc/udev/rules.d/99-oracle-asm-disk.rules
ACTION=="add|change", ENV{DM_UUID}=="mpath-3600a098038304635502b4d416652654a", SYMLINK+="ASM_OCR_1", OWNER="oracle", GROUP="oinstall", MODE="0660"
[server1]~#


####### TRIGGER UDEV

- Trigger udev and it will create related ASM devices 

/sbin/udevadm trigger --type=devices --action=add
/sbin/udevadm trigger --type=devices --action=change
/sbin/udevadm control --reload-rules