How can disk label get lost?

[Yong Huang]

$ cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.2 (Tikanga)
$ uname -a
Linux xxxxx 2.6.18-92.1.13.el5 #1 SMP Thu Sep 4 03:51:21 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux

Once in a while, blkid command shows missing LABEL for my device mapper disks VOL3 and VOL4:

$ blkid
...
/dev/mapper/asmvol2p1: LABEL="VOL2" TYPE="oracleasm"
/dev/mapper/asmvol1p1: LABEL="VOL1" TYPE="oracleasm"
/dev/sdp1: LABEL="VOL2" TYPE="oracleasm"
/dev/sdg1: LABEL="" TYPE="oracleasm"
/dev/sdf1: LABEL="" TYPE="oracleasm"
/dev/sdb1: LABEL="VOL2" TYPE="oracleasm"
/dev/sda1: LABEL="VOL1" TYPE="oracleasm"
/dev/mapper/asmvol3p1: LABEL="" TYPE="oracleasm"
/dev/mapper/asmvol4p1: LABEL="" TYPE="oracleasm"
/dev/sdh1: LABEL="VOL1" TYPE="oracleasm"
/dev/sdi1: LABEL="VOL2" TYPE="oracleasm"
/dev/sdm1: LABEL="" TYPE="oracleasm"
/dev/sdn1: LABEL="" TYPE="oracleasm"
/dev/sdo1: LABEL="VOL1" TYPE="oracleasm"
/dev/sdt1: LABEL="" TYPE="oracleasm"
/dev/sdu1: LABEL="" TYPE="oracleasm"
/dev/sdv1: LABEL="VOL1" TYPE="oracleasm"
/dev/sdw1: LABEL="VOL2" TYPE="oracleasm"
/dev/sdaa1: LABEL="" TYPE="oracleasm"
/dev/sdab1: LABEL="" TYPE="oracleasm"

Later blkid shows all labels correctly, without us doing anything.

$ blkid | egrep 'VOL3|VOL4'
/dev/sdg1: LABEL="VOL4" TYPE="oracleasm"
/dev/sdf1: LABEL="VOL3" TYPE="oracleasm"
/dev/mapper/asmvol3p1: LABEL="VOL3" TYPE="oracleasm"
/dev/mapper/asmvol4p1: LABEL="VOL4" TYPE="oracleasm"
/dev/sdm1: LABEL="VOL3" TYPE="oracleasm"
/dev/sdn1: LABEL="VOL4" TYPE="oracleasm"
/dev/sdt1: LABEL="VOL3" TYPE="oracleasm"
/dev/sdu1: LABEL="VOL4" TYPE="oracleasm"
/dev/sdaa1: LABEL="VOL3" TYPE="oracleasm"
/dev/sdab1: LABEL="VOL4" TYPE="oracleasm"

There's nothing in /var/log/messages. No cron job I know of that touches disk headers. What can be done to troubleshoot?

Oracle continues to function correctly, probably because once the database is up, the label is no longer needed, till the next database restart.

Yong Huang