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The Coexistence of the DMP and UltraPath for AIX Causes that the VCS Cluster Reports Reservation Errors Frequently

Publication Date:  2019-07-15 Views:  324 Downloads:  1

Issue Description

Product and version information:
 S2600
 S5000 series
 The operating system of application servers running AIX.
Disks that mapped from a storage device to an application server cannot be mounted on the application server. In addition, the VCS cluster reports reservation errors frequently.
The S5000 is used as an example. Figure 1-1 shows the networking mode of the VCS cluster under AIX.
Figure 1-1 Networking mode of the VCS cluster under AIX

1. After error logs on the application server are checked, a faulty disk is located. The disk is numbered hdisk98. The LUN ID of the corresponding storage device is 23. (hdisk98 is used as an example.)
2. Registered ports of the LUN are Port (35) and Port (44) on an array.
After the scsi getregister 23 command is executed in MML mode, the following command output is displayed:
spu ui>scsi getregister 23
Registrant: Nexus(568)  Port(35)  TargetPort(8)
Registrant: Nexus(712)  Port(44)  TargetPort(8)
LUN 23 has 2 registrants
The command output indicates that the LUN whose LUN ID is 23 registers two ports: Port (35) and Port (44).
3. After the tgt port show command is executed in the MML mode, the status of Port (35) and Port (44) can be viewed.
The following command output is displayed:
PortId:35    HostId:0  Type:0  Wwn:10000000c992d7cf    Name:Ap3fcs1 
PortId:44    HostId:1  Type:0  Wwn:10000000c99288f1    Name:Ap7fcs1
The command output indicates that WWNs of two reserved ports' HBAs are 10000000c992d7cf and 10000000c99288f1.
4. After the log information of the storage device is analyzed, the WWN of the port that has a reserved conflict is 10000000c992e2f7.
The error logs of the storage device are displayed as follows:
[20xx-xx-xx 17:34:15][25852170][15000000e004d][INFO][CONFLICT(0x2a 0x10000000c992e2f7 hostlun23 devlun23):Reserve conflict][SCSI][SCSI_Che.iction,679]
5. After the HBA information is checked on the application server, no reserved HBA is fcs3.
6. After the lspath -F"path_id:connection:parent:status" -l hdisk98 command is executed to check the connection status of hdisk98, the following command output is displayed:
7. After the priority of each path of disks is checked, the priority of the 3:22130022a10245e4,4000000000000:fscsi3:Enabled path is 1. (1 indicates the highest priority.) I/Os are transferred on this path. However, the VCS does not reserve the WWN (10000000c992e2f7) of the port on the HBA that corresponds to the path. Therefore, reservation errors are reported.
NOTE: The following command can be used to query the priority of a path:
lspath –l hdisk98 –p parent –w connection –F value –a priority, where parent corresponds to fscsi1 and fscsi2 in step 6 and connection corresponds to the connection field in the query results in step 6. 22020022a10245e4,4000000000000 is an example.

8. The DMP and UltraPath for AIX are installed on the application server.
The UltraPath for AIX scan all physical LUNs and generates corresponding virtual LUNs. The virtual LUNs are delivered to the DMP. The DMP detects only one path and sends only one reservation command to virtual LUNs. After a path that has the highest priority becomes faulty and recovers quickly, the path is not reserved.

Alarm Information


Handling Process

Step 1 Stop all services running on the application server.
Step 2 Run the unmount xxx command on the application server to uninstall the file system on a disk. xxx indicates the mount point of a file system.
NOTE: For example, if the file system that is mounted on /test needs to be uninstalled, run the unmount /test command.

Step 3 Run the varyoffvg xxx command on the application server to close the volume group (VG) where the disk resides. xxx indicates the name of a VG.
Step 4 Run the upadm remove array=xxx command on the application server to delete LUNs mapped by the storage device. xxx indicates a device model such as the S5000.
Step 5 Uninstall the UltraPath for AIX.
Step 6 Run the cfgmgr command on the application server to rescan for LUNs.
Step 7 Reset LUNs to enable them to be managed by the DMP.

Root Cause

The DMP and UltraPath for AIX exist together so that the VCS cluster reports reservation errors frequently.


It is risky if the DMP and UltraPath for AIX exist together in a VCS cluster. If an upper-layer application must use the DMP, you can uninstall the UltraPath for AIX.