DiskReservation Agent and reservation conflict error messages.

How the DiskReservation Agent works:

The Diskreservation agent is used to prevent access to a device(s). It does this by setting a scsi2 reservation on the device(s) this prevents other nodes from being able to access the device(s). Any access to the device via an ioctl call from any node that has not exclusively set the scsi2 reservation will return status RESERVATION CONFLICT. The error message will be logged to console and/var/log/messages. The scsi "reservation conflict" error message is from the scsi midlayer driver and the "diskres" driver cannot prevent this message from not occurring.

 

Note any 3rdparty application program, script or command that scans/probes a device(s)  which has a scsi2 reservation exclusively set will produce a"reservation conflict" error. Commands like vgscan, lvscan, fdisk, sfdisk,`vxdctl enable` are typicall commands that will scan/probe a device(s).

 

How theLVMVolumeGroup and LVMLogicalVolume agents use the DiskReservation agent:

TheLVMVolumeGroup and LVMLogicalVolume agent requires that the DiskReservation be configured. The DiskReservation resource is required because LVM Volume Groupsare always active on all nodes. This means that LVM Volume Groups are accessible on any node at any time. For VERITAS CLUSTER SERVER this is an issue as it would result in a Concurrency Violation. To workaround this problem theDiskReservation agent is used to ensure that only one node has access to the LVMVolume Group.

 

Workaround to minimize the errors produced by our VCS Agent monitor programs when using the DiskReservation agent in conjunction with LVMVolumeGroup and LVMLogicalVolumeagent resources.:

When OurLVMVolumeGroup and LVMLogicalVolume are configured under VERITAS Cluster Serverwe use LVM commands vgscan and lvscan to get the status of the resource(s)during the OfflineMonitorInterval, because the device(s) has SCSI2 reservationset the OfflineMonitorInterval will probe and the scsi midlayer driver willproduce errors and log to console and messages. You can alleviate the errors bydisabling the OfflineMonitorInterval or by extending the OfflineMonitorIntervalfrom default 300 (5 minutes) to 600 (10 minutes).

 

Disabling the OfflineMonitorInterval will prevent the scsi reservation conflict errorsfrom reporting to console and messages when the OfflineMonitor routine runs.

haconf-makerw

hatype-modify DiskReservation OfflineMonitorInterval 0

hatype-modify LVMVolumeGroup OfflineMonitorInterval 0

hatype-modify LVMLogicalVolume OfflineMonitorInterval 0

haconf -dump-makero

 

Toextend

haconf-makerw

hatype-modify DiskReservation OfflineMonitorInterval 600

hatype-modify LVMVolumeGroup OfflineMonitorInterval 600

hatype-modify LVMLogicalVolume OfflineMonitorInterval 600

haconf -dump-makero

 

What is theOfflineMonitorInterval:

- This is the duration (in seconds) between two consecutive monitor calls for an offlineresource. If set to 0, offline resources are not monitored.

- The default is 300 seconds for most resource types.

 

Veritas recommendation is to leave the default settings, but if the administrator wants to minimize the reservation conflict messages produced bye the scsi midlayer driver the above can be configured.