ASM diskgroup dismount with "Waited 15 secs for write IO to PST"

In this Document

APPLIES TO:

SYMPTOMS

CAUSE

Generally this kind messages comes in ASM alertlog file on below situations,

Delayed ASM PST heart beats on ASM disks in normal or high redundancy diskgroup,
thus the ASM instance dismount the diskgroup.By default, it is 15 seconds.

By the way the heart beat delays are sort of ignored for external redundancy diskgroup.
ASM instance stop issuing more PST heart beat until it succeeds PST revalidation,
but the heart beat delays do not dismount external redundancy diskgroup directly.

The ASM disk could go into unresponsiveness, normally in the following scenarios:

The Doc ID 10109915.8  briefs about Bug 10109915(this fix introduce this underscore parameter). And the issue is with no OS/Storage tunable timeout mechanism in a case of a Hung NFS Server/Filer. And then  _asm_hbeatiowait  helps in setting the time out.

SOLUTION

1]    Check with OS and Storage admin that there is disk unresponsiveness.

2]    Possibly keep the disk responsiveness to below 15 seconds. 

This will depend on various factors like
+    Operating System
+    Presence of Multipath ( and Multipath Type )
+    Any kernel parameter

So you need to find out, what is the 'maximum' possible disk unresponsiveness for your set up.

For example, on AIX  rw_timeout  setting affects this and defaults to 30 seconds.

Another example is Linux with native multipathing. In such set up, number of physical paths and  polling_interval value in multipath.conf file, will dictate this maximum disk unresponsiveness.

So for your set up ( combination of OS / multipath / storage ), you need to find out this.

3]    If you can not keep the disk unresponsiveness to below 15 seconds, then the below parameter can be set in the ASM instance ( on all the Nodes of RAC ):

    _asm_hbeatiowait
    
As per internal bug 17274537 , based on internal testing the value should be increased to 120 secs, the same will be fixed in 12.2

Run below in asm instance to set desired value for _asm_hbeatiowait

alter system set "_asm_hbeatiowait"= scope=spfile sid='*';

And then restart asm instance / crs, to take new parameter value in effect.

REFERENCES