ORACLE RAC Installation : Why there is a need to create a symbolic links for asm disk By reading the note 1538626.1 from MOS Meta Link, I know that we should use udev to change the ownership of some device for the further installation of oracle real application cluster:
I met a lot of similar udev rules for the purpose of changing the owner of asm disk  in internet as follow:

ENV{DM_NAME}=="data01", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="data02", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="data03", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="data04", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="crs01", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="crs02", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="crs03", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"


After the rules is defined, we can restart the udev and get the device with ownership changed

#ls -l /dev/dm*
brw-rw---- 1 root    disk     253,  0 Dec 15 14:18 /dev/dm-0
brw-rw---- 1 root    disk     253,  1 Dec 15 14:18 /dev/dm-1
brw-rw---- 1 root    disk     253, 10 Dec 15 14:18 /dev/dm-10
brw-rw---- 1 oragrid asmadmin 253,  2 Dec 15 14:18 /dev/dm-2
brw-rw---- 1 oragrid asmadmin 253,  3 Dec 15 14:18 /dev/dm-3
brw-rw---- 1 oragrid asmadmin 253,  4 Dec 15 14:18 /dev/dm-4
brw-rw---- 1 oragrid asmadmin 253,  5 Dec 15 14:18 /dev/dm-5
brw-rw---- 1 oragrid asmadmin 253,  7 Dec 15 14:18 /dev/dm-7
brw-rw---- 1 oragrid asmadmin 253,  8 Dec 15 14:18 /dev/dm-8
brw-rw---- 1 oragrid asmadmin 253,  9 Dec 15 14:18 /dev/dm-9


At the same time, because we use the key SYMLINK in the udev rules, we can get the symbolic links which act as alternative names for the device node

#  ls -l /dev/iscsi/*
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-crs01 -&gt; ../dm-5
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-crs02 -&gt; ../dm-7
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-crs03 -&gt; ../dm-8
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data01 -&gt; ../dm-9
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data02 -&gt; ../dm-2
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data03 -&gt; ../dm-3
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data04 -&gt; ../dm-4


It seems that such SYMLINK has no relationship with the rac installation, why is the purpose of adding the sysmlink property in the udev rules?Can I get rid of sysmlink in the udev rules?
It is not mandatory, do not use it if you do not want to.

Creating such symlinks just makes it easier to distinguish the ASM disks. You can even set asm_diskstring to /dev/iscsi/* with the above.