RAC Install – How to check if the disks are shared across nodes

Before installing RAC, we need to make sure that the disks are actually shared across the nodes. Normally sysadmins will present and share disks. I normally check the ‘shared’ aspect using following process.

NOTE: Cluvfy script will check this for us. This is additional level of checking.

— First check physical devices. In few cases Major/Minor could be different. So we can’t rely on this.

grid@rac-node1:/dev> ls -al | grep sdi
brw-rw---- 1 oracle oinstall 8, 128 2012-09-13 11:35 sdi
grid@rac-node2:/dev> ls -al | grep sdi
brw-rw---- 1 oracle oinstall 8, 128 2012-09-13 11:35 sdi

NOTE: Major, Minor numbers allow device mapping with hardware drivers. Each driver has a number called the major number. OS kernel uses major number to identify which driver to use.

Following check will actually perform a write/read test for a device from different nodes.

— NODE 1

grid@rac-node1:~> echo "NODE 1" > text.txt

grid@rac-node1:~> dd if=text.txt of=/dev/sdi count=1
0+1 records in
0+1 records out
7 bytes (7 B) copied, 3.4667e-05 s, 202 kB/s

— NODE 2

grid@rac-node2:~> dd if=/dev/sdi of=text.txt count=1
1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.00843018 s, 60.7 kB/s

*** Here we should see the text written from NODE 1

grid@rac-node2:~> cat text.txt
NODE 1

grid@rac-node2:~> echo "NODE 2" > text.txt

grid@rac-node2:~> dd if=text.txt of=/dev/sdi count=1
0+1 records in
0+1 records out
7 bytes (7 B) copied, 0.000358504 s, 19.5 kB/s

— NODE 1

grid@rac-node1:~> dd if=/dev/sdi of=text.txt count=1
1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.00028609 s, 1.8 MB/s

*** Here we should see the text written from NODE 2

grid@rac-node1:~> cat text.txt
NODE 2
Advertisements
This entry was posted in Oracle Real Application Cluster and tagged , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s