ASM Diskstring default values

In case you have trouble getting the newly added disks to your ASM instance check for the ASM_DISKSTRING init paramter. If ASM_DISKSTRING is NOT SET then the following default is used

Default ASM_DISKSTRING per Operating System

Operating System Default            Search String
=======================================
Solaris (32/64 bit)                        /dev/rdsk/*
Windows NT/XP                          .orcldisk*
Linux (32/64 bit)                          /dev/raw/*

LINUX (ASMLIB)                         ORCL:*
LINUX (ASMLIB)                        /dev/oracleasm/disks/*

HPUX                                             /dev/rdsk/*
HP-UX(Tru 64)                            /dev/rdisk/*
AIX                                                 /dev/*

IF ASM_DISKSTRING is SET  then we should verify that the setting includes the disks that are needed to be seen by ASM.

Source from :  https://abchatur.wordpress.com/2011/09/01/asm-diskstring-default-values/