Re: HACMP failed over on loss of mirrored rootvg
- From: Robert Binkley <leebinkley@xxxxxxxxx>
- Date: Mon, 17 Jul 2006 12:23:28 -0700
The failure for hdisk0 should be logged in the errpt
-a command, also verify that all rootvg file system
and paging space is accessable
Put the disks on separate controllers if at all
possible. you need to mirror all logical volumes which
your application uses. The last time that we checked,
all applications use the operating system and the
operating system (i.e. AIX) uses rootvg logical
volumes so mirror them. One that is sometimes missed
is the paging space. Mirror the paging space if you
want your node to be able to survive the loss of a
physical volume containing paging space (i.e. if you
don't mirror it then you've got a single point of
failure).
Most existing HACMP clusters are configured to send
system dumps to the primary paging space. Some (all?)
versions of AIX won't generate a system dump into a
mirrored paging space. Create a separate unmirrored
dump space if this restriction applies to your version
of AIX (assume that it does if you aren't sure). Even
if AIX supported them, a mirrored dump space would be
a waste of disk space since you won't need it unless
the AIX kernel crashes and a kernel crash combined
with a disk failure is either a double failure or was
almost certainly caused by the disk failure.
Another factor to consider is that AIX doesn't respond
well if an unmirrored rootvg physical volume is lost.
Basically what happens is that the parts of AIX which
notice the problem either hang or are terminated by
the disk errors. The end result is that the operating
system's features and facilities gradually stop
working until, eventually, someone notices (i.e. a
human) or something critical terminates (if the HACMP
cluster manager is ever affected (rather unlikely but
it happens) then the node will die about fifteen
seconds later. Either eventuality could take a LONG
time (think in terms of hours of elapsed time) during
which random parts of your application will have
probably either terminated or hanged.
Bottom line: mirror rootvg. Use the mirrorvg command
and then follow the extra steps described in the
mirrorvg man page for your version of AIX.
Regards
Robert Lee binkley
Dimler Chrysler
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- HACMP failed over on loss of mirrored rootvg
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