This article will introduce the recommended method of how to create an access group after we already created a VTL in Data Domain.

When you create an access group, need to pay attention to the following points:

Media server and operating system:

1.  What is the backup media server's operating system? When adding the backup media, it is usually to add an operating system server when you create each group, or each group is assigned a client or HBA.

2.  How many backup media server requires access to the same tape drive? If possible, it is best to assign different drives to different clients to avoid device sharing.

3.  If your backup software does not use the "share storage" option, it is best to create a separate access group for each client, and each group is assigned a unique tape drives to each client server.

Drive and Autochanger (Robotic arm)

1.  Avoid assign Autochanger to each access group. In general, only the primary backup server should access Autochanger.

2.  Avoid multiple Autochangers in the same access group.

3.  When assigning VTL FC port, you must first determine which target port is connected with initiator port on host. Use the following command to get the connection status between initiator port and target port on DD:

# scsitarget initiator show detailed

Initiator       Status   Endpoint

-------------   ------   -------------

initiator-1     Online   endpoint-fc-0

initiator-2     Online   endpoint-fc-1

-------------   ------   -------------

Please avoid to using "all" for primary or secondary port. Usually assign a primary or secondary port. If an initiator port is connected to a single target port, then select the single target port as the primary port. If an initiator is connected to multiple target ports, then select one target port as the primary port.

4.  Avoid sharing the same tape drive or Autochanger to multiple access group.

LUN addressing:

1.  In most cases, it is best to allow VTL LUN ID is automatically assigned, you don’t need to fill in LUN ID when create an access group. In addition, when assigning LUN ID, we recommend assign ID in proper order, otherwise will cause access problems for some operating systems.

2.     Use NAS or any Linux OS based server: When assigning access to Linux machines, always use LUN zero as the first LUN in the group, and use contiguous LUN numbers starting at zero with no gaps in the sequence.  For example, assigning LUNs 0, 1, 2, 3, 4 is correct, assigning LUNs 0, 2, 4, 5 is incorrect. Always use one primary path on the VTL HBA to the tape drives and Autochanger for the access group.

3.     Tivoli Storage Manager (TSM):  For TSM servers or clients, assign only one specific primary port to a tape drive or Autochanger, and don’t assign more than one primary port to a tape drive or Autochanger.

4.     AS/400:  For AS/400 installations adhere to the same policy as for TSM, by assigning only one primary port to a tape drive or Autochanger.  It is important to avoid assigning more than one primary port to a tape drive or Autochanger. You can use alternating ports for alternating LUNs so it is perfectly OK to use primary port 4a for LUNs 0, 2, 4, 6, 8 and primary port 4b for LUNs 1, 3, 5, 7 as long as the client using this group is not a LINUX machine or a NAS filer.

5.     HP/UX:  For HP-UX there are several things to consider and there is a whole KB article devoted just to using HP-UX.

6.     Solaris:  For Solaris you can spread out the primary paths among the LUNs, as Solaris does not have to see a LUN zero on every path. So for example for LUNs 0, 1, 2, 3, 4, 5 you can assign primary port 4a for LUNs 0, 2, 4, 6, 8 and primary port 4b for LUNs 1, 3, 5, 7.

7.     Windows: You can use the same port assignments for Windows as described for Solaris, above.

8.     IBMi systems (AS400): Some customers want to use a single library across multiple LPARS or systems, or to use multiple HBAs on the IBMi system. In these cases, follow these guidelines::

1)     Split the drives across multiple access groups each addressing a single IBMi HBA.

2)     Add the Autochanger to each group. The Autochanger will be visible over multiple paths and the library will appear with multiple names on the IBMi system.

The library and drive access can now be controlled from the WRKMLBSTS level on the IBMi system. By varying on and off the individual instances of the library on the IBMi the customer can control how the library is accessed.

Special requirements regarding backup software:

Please consult your backup application’s documentation to determination if your software has any of the following limitations:

·    Some backup software may have limitations in the number of tape drives it can recognize being attached to a client or server.

·    Some backup software may have a limit on the number of slots it can accommodate.

·    Some backup software cannot arbitrate multiple clients accessing common resources so those require unique tape drives in each access group and single server/client per group.

Author: Leo