EMC PowerPath: superblock could not be read

How to get around a simple setup issue where fsck tries to check a SAN disk before EMC PowerPath starts

Written by Benjamin Cane on 2013-06-05 | 1 min read

Recently while working on a system that uses EMC PowerPath, I ran into a little issue after rebooting.

The Issue

fsck.ext3: No such file or directory while trying to open /dev/emcpowera1
/dev/emcpowera1:
The superblock could not be read or does not describe a correct ext2 filesystem.

The Cause

The root cause of this issue is pretty simple when a Linux system boots it performs file system checks on file systems listed within the /etc/fstab file. When my system reached the /boot file system which has a device of /dev/emcpowera1, it could not find that device. Therefore the system could not perform a check and went into maintenance mode.

The reason /dev/emcpowera1 is not found is because PowerPath has not started yet. When a Red Hat based system is booting after the init process is spawned it will execute the /etc/rc.sysinit script. Within that file are the commands to both start PowerPath and run a file system check on all of the file systems listed in /etc/fstab.

# grep Power rc.sysinit
# Configure and initialize PowerPath.
if [ -f /etc/init.d/PowerPath ]; then
/etc/init.d/PowerPath start

Unfortunately the snippet that starts PowerPath is listed after the file system checks are initiated.

The Fix

The resolution for this problem is simple; disable boot time file system checks on anything that references an EMC PowerPath device. To do this I will edit the /etc/fstab and change the passno field to 0

# vi /etc/fstab

Find:

#device mount_point fstype options dump_freq passno
/dev/emcpowera1 /boot ext3 defaults 1 2

Modify To:

#device mount_point fstype options dump_freq passno
/dev/emcpowera1 /boot ext3 defaults 0 0

Now the next time the system boots it will skip the /boot file system check and boot without any errors.

As a note: I also changed the dump_freq to 0 on my system not because I had to for file system checks but because in my environment I will not need any dump backups of the file system.


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Benjamin's specialty is keeping the lights on for mission critical systems. He is currently building applications that enable high concurrency financial transactions.

Recently Benjamin published his first book; Red Hat Enterprise Linux Troubleshooting Guide. In addition to writing, he has several Open Source projects focused on making Ops easier. These projects include Automatron, a project enabling auto-healing infrastructure for the masses.


Publications

Identify, capture and resolve common issues faced by Red Hat Enterprise Linux administrators using best practices and advanced troubleshooting techniques

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