There is a serious vulnerability for Oracle RAC
databases noted in the Oracle 11g Release 2 RAC documentation.
This note indicates a possible scenario where it's possible for
an entire RAC cluster to fail.
This exposure is only for RAC databases that are using Automatic
Storage Management (ASM).
This is new in 11g Release 2, and see here for
details on the
ACFS, the ASM cluster filesystem for RAC.
When using RAC, Oracle has announced that the key
clusterware files, the OCR and Votedisks, can now be stored in Oracle
Automated Storage Management (ASM).
However, research by our BC expert DBA's indicate that
it may well be premature to use this feature.
According to Oracle's documentation, the 11gR2
Clusterware Administration and Deployment Guide (chapter 2) , if a
single node is lost, then the entire cluster may go down, if that node
happens to be the master node.
The quote from the guide is this:
"If Oracle
ASM fails, then OCR is not accessible on the node on which Oracle ASM
failed, but the cluster remains operational.
The entire
cluster only fails if the Oracle ASM instance on the OCR master node
fails, if the majority of the OCR locations are in Oracle ASM, and if
there is an OCR read or write access, then the
crsd stops and
the node becomes inoperative."
In order to identify the OCR master node, search
the crsd.log file for the line "I AM THE NEW OCR MASTER" with the most
recent timestamp.
Oracle has also announced that new installations of
11gR2 (as opposed to upgrades) will not allow the installation of the
OCR and Votedisks on RAW, so the best solution at this time is to
install these files on a shared, non-ASM filesystem such as OCFS2.
Clusterware upgraded to 11gR2 may still be on RAW.
Click here to learn more secrets about using ASM
with Oracle RAC:
http://www.rampant-books.com/book_2004_1_10g_grid.htm
http://www.dba-oracle.com/t_using_20_adm_rac_clusters.htm
http://www.dba-oracle.com/real_application_clusters_rac_grid/limitations_asm.htm
and include the URL for the page.
