Application Notes Linux Device Mapper Multipath with Data Replication Solutions for HP StorageWorks EVA and XP disk arrays (5697-7807, October 2008)

Figure 1 Local replication environment

Business Copy with HP StorageWorks Enterprise Virtual Arrays

Business Copy solution enables you to create Snapclones, Snapshots, and Mirrorclones for local data

replication. Linux Device M apper Multipath supports usage of the data c opies in a multipathed SAN

environment. When a Business Copy object such as Snapclone or Snapshot of a Vdisk is created and

discover

ed from the host, a new multipath device is created under the directory / dev/mapper.

The multipath device of the Business Copy object will inherit the multipath conﬁgura tion of the a rray. This

multipath device would b e available for read/write operations d epending on the host access permission

of the Business Copy object.

Mirrorclones account for another variety of Business Copy object for lo cal da ta replication. Mirrorclone

object i

s transparent and it cannot be presented to the host in the “synchronized” state. In a “Fractured” or

“Detached” state, mirrorclone object can be presented to the host and a multipath device will be created.

Business Copy with HP StorageWorks XP disk arrays

Local data replication is achieved throu gh the creation of pair where the original and backup volumes

are termed as P-VOL and S-VOL resp ectively. Pairs are created using the paircreate operation and the

data resident on P-VOL is copied to S-VO L in the destination array. The S-VOL is not available for read

and write operation in a PAIR state.

S-VOL can be made available for read and write operations by suspending the pair using the pa irsplit

operation and the volumes are in a PSUS state. Data in the S-VOL can be resynchronize d with the P-VOL

using the pairresync operation after which the S-VOL is not available for read or write operations.

Device Mapper Multipath devices will be created for Business Copy objects and will inherit the multipath

conﬁguration of the array. The multipath device would be available for read/write operations depending

onthehostaccesspermissionoftheBusinessCopyobject.

Recognizing host access permission changes of a Logical Unit

Host access permission of a Logical Unit (LU) can be changed using the management appliance. To

recognize this change from the host, execute the following steps:

1. Ensure the multipath device is not in use.

2. Dele

te the multipath device c orresponding to the LU.

#multipath –f <mpath device>

3. Rescan all the SCSI devices to recognize the permission change.

Linux Device Mapper Multipath with Data Replication Solutions for HP StorageWorks EVA and XP disk arrays