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

Site failover
Failover of data
from the source array to the destination array m ay be a planned or unplanned. Planned
failover of source array may b e due to a scheduled downtime at the local site like hardware maintenance,
application maintenance, which needs the operations to be moved from local site to the remote site.
Unplanned fail
over may be due to an unexpected loss of local s ite, d ue to hardware failure, natural
disasters where the hardware components at the local site may not remain intact.
In such scenarios, on failover, the destination array is switched to become a source array. The source array
behavesasades
tination array, when it becomes available. On failover of the DR group, the read/write
permission of
the LUs which are p art of the DR group is changed from read-only to read-write on the
destination a
rray and from read-write to read-only on the source array, if the source array is available.
This permission change is required to be recognized by the host. To recognize this change from the host,
execute the following steps:
1. Ensure the multipath device is not in use.
2. Delete the mu
ltipath device c orresponding to the LU.
#multipath –f<mpath device>
3. Rescan all the SCSI devices to recognize the permission change.
#echo 1 > /sys
/block/<SCSI device>/device/rescan
4. Create multipath devic e for the LU with the new host access permission.
#multipath –v0
Deleting Data Replication groups
Deleting a DR group, results in the disassociation of the source Vdisk from the destination. The destination
Vdisk is switched to a stand a lone Vdisk which will be available for read and write opera tions.
To delete a DR group, complete the following steps at the destination site. If all the below mentioned
commands are not executed, LUN collision may occur. LUN collision results in the creation of a new
LUN through old devic e special files since the new LUN is presented in the same SCSI slot, which may
lead to d a ta corruption.
1. Ensure the Vdisks, which are part of the DR group are not in use.
2. Remove the multipath devices corresponding to the Vdisks.
#multipath –f<mpath device>
3. Delete the SCSI devices corresponding to the paths of the multipath device.
#echo 1>/sys/block/<SCSI device>/device/delete
4. Unpresent the Vdisks from the host, using storage management appliance.
5. Delete the DR group from the storage mana gement appliance.
On deleting a DR group, the WWN of the destination Vdisk is changed to a new unique WWN,
different from the WWN of the source Vdisk.
1. If necessary, present the Vdisk to the host using the management appliance.
2. Discover the pa ths to the Vdisk.
#hp_rescan –a
3. Create multipath device with the new Vdisk WWN.
#multipath –v0
Refer en
ces
• Devic e Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays Installation and
Reference Guide
h
ttp:/
/www.hp.com/go/devicemappe r
• HP StorageWorks Business Copy EVA administrator guide
Linux Device Mapper Multipath with Data Replication Solutions for HP StorageWorks EVA and XP disk arrays
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