zpool export/import on failover - The pool metadata is corrupted

[mxb]

Sure, script is not perfects yet and does not handle many of stuff, but moving highlight from zpool import/export to the script itself not that
clever,as this works most of the time.

Question is WHY ZFS corrupts metadata then it should not. Sometimes.
I'v seen stale of zpool then manually importing/exporting pool.


On 7 jun 2013, at 00:39, Jeremy Chadwick <jdc at koitsu.org> wrote:

> On Fri, Jun 07, 2013 at 12:12:39AM +0200, mxb wrote:
>> 
>> Then MASTER goes down, CARP on the second node goes MASTER (devd.conf, and script for lifting):
>> 
>> root at nfs2:/root # cat /etc/devd.conf
>> 
>> 
>> notify 30 {
>> match "system"		"IFNET";
>> match "subsystem"	"carp0";
>> match "type"		"LINK_UP";
>> action "/etc/zfs_switch.sh active";
>> };
>> 
>> notify 30 {
>> match "system"          "IFNET";
>> match "subsystem"       "carp0";
>> match "type"            "LINK_DOWN";
>> action "/etc/zfs_switch.sh backup";
>> };
>> 
>> root at nfs2:/root # cat /etc/zfs_switch.sh
>> #!/bin/sh
>> 
>> DATE=`date +%Y%m%d`
>> HOSTNAME=`hostname`
>> 
>> ZFS_POOL="jbod"
>> 
>> 
>> case $1 in
>> 	active)
>> 		echo "Switching to ACTIVE and importing ZFS" | mail -s ''$DATE': '$HOSTNAME' switching to ACTIVE' root
>> 		sleep 10
>> 		/sbin/zpool import -f jbod
>> 		/etc/rc.d/mountd restart
>> 		/etc/rc.d/nfsd restart
>> 		;;
>> 	backup)
>> 		echo "Switching to BACKUP and exporting ZFS" | mail -s ''$DATE': '$HOSTNAME' switching to BACKUP' root
>> 		/sbin/zpool export jbod
>> 		/etc/rc.d/mountd restart
>>                /etc/rc.d/nfsd restart
>> 		;;
>> 	*)
>> 		exit 0
>> 		;;
>> esac
>> 
>> This works, most of the time, but sometimes I'm forced to re-create pool. Those machines suppose to go into prod.
>> Loosing pool(and data inside it) stops me from deploy this setup.
> 
> This script looks highly error-prone.  Hasty hasty...  :-)
> 
> This script assumes that the "zpool" commands (import and export) always
> work/succeed; there is no exit code ($?) checking being used.
> 
> Since this is run from within devd(8): where does stdout/stderr go to
> when running a program/script under devd(8)?  Does it effectively go
> to the bit bucket (/dev/null)?  If so, you'd never know if the import or
> export actually succeeded or not (the export sounds more likely to be
> the problem point).
> 
> I imagine there would be some situations where the export would fail
> (some files on filesystems under pool "jbod" still in use), yet CARP is
> already blindly assuming everything will be fantastic.  Surprise.
> 
> I also do not know if devd.conf(5) "action" commands spawn a sub-shell
> (/bin/sh) or not.  If they don't, you won't be able to use things like"
> 'action "/etc/zfs_switch.sh active >> /var/log/failover.log";'.  You
> would then need to implement the equivalent of logging within your
> zfs_switch.sh script.
> 
> You may want to consider the -f flag to zpool import/export
> (particularly export).  However there are risks involved -- userland
> applications which have an fd/fh open on a file which is stored on a
> filesystem that has now completely disappeared can sometimes crash
> (segfault) or behave very oddly (100% CPU usage, etc.) depending on how
> they're designed.
> 
> Basically what I'm trying to say is that devd(8) being used as a form of
> HA (high availability) and load balancing is not always possible.
> Real/true HA (especially with SANs) is often done very differently (now
> you know why it's often proprietary.  :-) )
> 
> -- 
> | Jeremy Chadwick                                   jdc at koitsu.org |
> | UNIX Systems Administrator                http://jdc.koitsu.org/ |
> | Making life hard for others since 1977.             PGP 4BD6C0CB |
>