Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax and VMAX: Non-Disruptive and Minimally Disruptive Migration Best Practices and Operational Guide > Overview
O-MDM (Open Minimally Disruptive Migration) utilizes Open Replicator (ORS) as the data transfer mechanism instead of native SRDF/Metro used by NDM. ORS is a SCSI block migration feature that transfers data from an external array through a WWN designated FBA source device.
As such, it is extremely flexible in the source arrays supported:
ORS integration supports the familiar create/cutover/commit as a typical NDM migration. Source array devices are presented to PowerMax front end FA ports through the donor array native provisioning mechanism. The symsan SYMCLI command can be used to verify PowerMax visibility on these devices.
New symdm command syntax, create –san –offline, is used to initiate a new O-MDM migration session. This new command syntax requires a new option (-file) specifying the input of a file containing a list of donor device WWNs familiar to ORS users. Target devices, associated SGs, and front-end host mapping are then created. Target devices created on the PowerMax are rounded to the nearest cylinder size.
Similarly, Unisphere 10.0 includes a SAN WWNS tab from the Data Protection -> Migration option for initiating and managing O-MDM migrations:
Prior to the cutover command, the source application must be shut down (minimally disruptive). After a cutover command, target devices from PowerMax are made visible to the host. Applications can then be restarted now that they are sourced from the PowerMax. ORS Donor Update is then used to keep the source devices/array updated.
Commit can then be initiated to stop the migration session and associated ORS Donor Update session to source devices.
The SYMCLI symdm command syntax has changed, with the following new options (highlighted in bold text) to support the O-MDM functionality:
symdm -tgt_sid <SymmID>
[-i <Interval>] [-c <Count>] [-noprompt]
[-tgt_srp <SRPName>] [-tgt_pg <PgName>]
[-nocompression] [-validate]
create –src_sid <SymmID> -sg <SgName> [-precopy]
create –src_sid <SymmID> -sg <SgName>
-offline [-move_identity] [-precopy]
create –file <FileName> -tgt_sg <SgName>
-tgt_ig <IgName> –san -offline
Options: