Thursday, February 2, 2012

ASMLib and EMC PowerPath Multipathing


Another quick note - an email I sent to other DBAs at work.

Problem - ASMLib picks the first disk device it finds for a particular ASM disk and uses that device. This usually means that ASM is NOT using the multipath emcpower device.

ASMLib picks the first disk device it finds for a particular ASM disk and uses that device. This usually means that ASM is NOT using the multipath emcpower device. 

Let's pick an ASMLib disk on my server - in this case I choose a disk that has been named  ORA_FPF_90GB_EMCP022 .

root@fpfkxtdb02 ~# /etc/init.d/oracleasm  querydisk ORA_FPF_90GB_EMCP022 
Disk "ORA_FPF_90GB_EMCP022" is a valid ASM disk 

There are lots of possible paths to the disk. ASM picks the first one it finds and ignores the rest. What paths are there for our disk?? 

root@fpfkxtdb02 ~# /etc/init.d/oracleasm querydisk -p ORA_FPF_90GB_EMCP022 
Disk "ORA_FPF_90GB_EMCP022" is a valid ASM disk 
/dev/sdn1: LABEL="ORA_FPF_90GB_EMCP022" TYPE="oracleasm" 
/dev/sdav1: LABEL="ORA_FPF_90GB_EMCP022" TYPE="oracleasm" 
/dev/sdcd1: LABEL="ORA_FPF_90GB_EMCP022" TYPE="oracleasm" 
/dev/sddk1: LABEL="ORA_FPF_90GB_EMCP022" TYPE="oracleasm" 
/dev/emcpowerm1: LABEL="ORA_FPF_90GB_EMCP022" TYPE="oracleasm" 

Lots of paths.

Lets see what device path is actually being used for our ASMLib disk: 

root@fpfkxtdb02 ~# /etc/init.d/oracleasm querydisk -d ORA_FPF_90GB_EMCP022 
Disk "ORA_FPF_90GB_EMCP022" is a valid ASM disk on device [8, 209] 

Device [8, 209]  is the first disk in the path list - /dev/sdn1 - NOT the emcpower device. 

root@fpfkxtdb02 ~# ls -l /dev/sdn1 
brw-r----- 1 root disk 8, 209 Oct 24 12:15 /dev/sdn1 

We want ASMLib to be using THIS device: 

root@fpfkxtdb02 ~# ls -l /dev/emcpowerm1 
brw-r----- 1 root disk 120, 193 Oct 24 12:15 /dev/emcpowerm1 

HOW TO FIX IT SO THAT THE EMCPOWER DEVICE IS THE DEVICE THAT ASMLIB USES

Edit ORACLEASM_SCANORDER and ORACLEASM_SCANEXCLUDE!

root@fpfkxtdb02 ~# vim /etc/sysconfig/oracleasm 

Change

# ORACLEASM_SCANORDER: Matching patterns to order disk scanning 
ORACLEASM_SCANORDER="" 

# ORACLEASM_SCANEXCLUDE: Matching patterns to exclude disks from scan 
ORACLEASM_SCANEXCLUDE="" 


TO

# ORACLEASM_SCANORDER: Matching patterns to order disk scanning 
ORACLEASM_SCANORDER="emcpower" 

# ORACLEASM_SCANEXCLUDE: Matching patterns to exclude disks from scan 
ORACLEASM_SCANEXCLUDE="sd dm" 



Unload, reload ASM and scandisks

root@fpfkxtdb02 ~# oracleasm exit 
Unmounting ASMlib driver filesystem: /dev/oracleasm 
Unloading module "oracleasm": oracleasm 
root@fpfkxtdb02 ~# oracleasm init 
Loading module "oracleasm": oracleasm 
Mounting ASMlib driver filesystem: /dev/oracleasm 
root@fpfkxtdb02 ~# /etc/init.d/oracleasm scandisks 
Scanning the system for Oracle ASMLib disks:               [  OK  ] 


Check that ASM is now using the emcpower device:


root@fpfkxtdb02 ~# /etc/init.d/oracleasm querydisk -d ORA_FPF_90GB_EMCP022 
Disk "ORA_FPF_90GB_EMCP022" is a valid ASM disk on device [120, 193] 

Done


No comments:

Post a Comment