Recommendations and guidelines for online disk removal, addition and replacement procedures for HPUX 11.31/VxVM 5.0

Recommendations and guidelines for online disk removal, addition and replacement procedures
for HPUX 11.31/VxVM 5.0

VxVM 5.0 introduces a new tunable "dmp_cache_open" as described below.

dmp_cache_open

If set to on, the first open of a device that is performed by an array support
library (ASL) is cached. This enhances the performance of device discovery by
minimizing the overhead caused by subsequent opens by ASLs. If set to off,
caching is not performed.

The value of this tunable is changed by using the vxdmpadm settune command.

This tunable  has considerable impact on the procedure required for VxVM "dynamic reconfiguration" (DR) when performing online disk addition, deletion, and/or replacement which may result in a change of the instance number of disk paths in the OS IO tree. Such DR procedures may occur quite often on systems when disks are added and cloned and later removed periodically for backup purpose.


To ensure that VxVM/DMP is aware of any dynamic instance number changes, important DR steps must be followed.
It is critical to follow the procedures outlined below  to ensure that VxVM/DMP is aware of, and maintains consistency during the dynamic re-assignment of instance numbers during online disk replacement/addition/deletion.


For VxVM 5.0/11.31 systems, it is recommended that dmp_cache_open be turned on (enabling "DMP open caching") before any DR procedure and be retained at the ON setting even after the completion of the DR procedure.
The default value of the tunable will be reverted to the recommended 'ON' setting in an upcoming patch.

The following enhanced DR procedures will be added to VxVM 5.0/11.31 Administration Guide.

Note: All disks connected to the system are by default under DMP control unless they are specifically excluded from DMP control via vxdiskadm(1M) or by declaring them a foreign disk with vxddladm(1M). Regardless of whether these disks are formatted for VxVM usage, DMP will still scan and claim these disks. As a result, the following DR procedures should be followed even for disks that are not formatted as VxVM disks.


Disk Replacement Procedure - Online LUN Removal

Step 1: Enable DMP open caching
vxdmpadm settune dmp_cache_open=on
Step 2: Identify the LUNs to be removed from the host, using:
vxdisk -e -o alldgs list
Step 3: Remove disks from diskgroup:
vxdg -g <diskgroup-name> rmdisk <dm-name>
Step 4: Close and remove the LUNs at the VxVM layer
vxdisk rm <da-name>
Step 5: Mask/Remove the LUNs at the Storage Layer, clean up the OS device tree (e.g. with rmsf)
Step 6: Update VxVM
vxdisk scandisks



Disk Replacement Procedure - Online LUN Addition


Step 1. Enable DMP open caching
vxdmpadm settune dmp_cache_open=on
Step 2. Add the LUNs
Step 3. Perform OS device discovery so that LUNs are visible to the OS (e.g. ioscan, insf)
Step 4. Update VxVM
vxdisk scandisks

Disk Replacement Procedure - Online LUN Replacement

Step 1. Enable DMP open caching
       vxdmpadm settune dmp_cache_open=on
Step 2: Identify the LUNs to be replaced from the host, using:
       vxdisk -e -o alldgs list
Step 3: Remove disks from diskgroup:
       vxdg -g <diskgroup-name> rmdisk <dm-name>
Step 4: Close and remove the LUNs at the VxVM layer
       vxdisk rm <da-name>    
Step 5: Mask/Remove the LUNs at the Storage Layer, clean up the OS
device tree (e.g. with rmsf)
Step 6: Add the replacement LUNs
Step 7. Perform OS device discovery so that LUNs are visible to the OS
(e.g. ioscan, insf)
Step 8. Update VxVM
       vxdisk scandisks