Logical units and target ports on MSA2000 systems

Partitions (volumes) on MSA2000 systems are exported as logical units with a logical unit number that is assigned to that partition.

LUNs on MSA2000 systems

The controller calls an array a volume. SAS and SATA disks cannot be mixed within a volume, and the maximum number of volumes per controller is 16. Volumes can be divided into volumes, which are then presented to the host. There can be up to 128 volumes per controller. The capacity of a volume is 1 MB - 16 TB.

Storwize V5000 has an individual 1 PB managed-disk size limit.

LUN IDs

LUNs exported by MSA2000 systems report identification descriptors 0, 3, 4, 5 in the VPD page 0x83. The LUN IDs are based on the controller MAC addresses. For example:

example;
# show volumes
Vdisk    Volume Name   Size  WR Policy    Class  Volume Serial Number  Cache Opt  Type

VD0                    VD0_V1               750.1GB  writeback    standard 00c0ffd76a330000a0fa124a01000000  standard  standard
VD2                    VD2_V1               750.1GB  writeback    standard 00c0ffd76a33000048fb124a01000000  standard  standard
VD_HC                  VD_CAP_V1            37.5GB   writeback    standard 00c0ffd76a3300005efc124a01000000  standard  standard
VD_1                   VD_1_V1              750.1GB  writeback    standard 00c0ffd7648f000064851d4a01000000  standard  standard
VD_3                   VD_3_V1              750.1GB  writeback    standard 00c0ffd7648f0000a6851d4a01000000  standard  standard
VD-R                   VD-R_V1              250.0GB  writeback    standard 00c0ffd7648f0000aa08234a01000000  standard  standard
VD-R                   VD-R_V2              250.0GB  writeback    standard 00c0ffd7648f0000ab08234a01000000  standard  standard
VD-R                   VD-R_V3              250.0GB  writeback    standard 00c0ffd7648f0000ab08234a02000000  standard  standard
------------------------------------------------------------------------------------------------------------------------
# show network-parameters
Network Parameters Controller A
-------------------------------
IP Address     : 9.71.47.27
Gateway        : 9.71.46.1
Subnet Mask    : 255.255.254.0
MAC Address    : 00:C0:FF:D7:6A:33
Addressing Mode: DHCP

Network Parameters Controller B
-------------------------------
IP Address     : 9.71.47.30
Gateway        : 9.71.46.1
Subnet Mask    : 255.255.254.0
MAC Address    : 00:C0:FF:D7:64:8F
Addressing Mode: DHCP

LUN creation and deletion

MSA2000 LUNs can be created, modified, or deleted either by the Storage Management Utility (SMU) or the command-line interface (CLI). LUNs can be used immediately with format to zeros as default background task.

Note: Disks appear as critical while this process is taking place.

To create a logical unit (or volume), complete these steps:

In the Storage Management Utility SMU interface, go to Manage > Virtual Disk Config > Create a VDisk. The SMU provides a wizard to create the volume.
You have the following options:
- Manual
- Volume Name
- RAID Type
  Note: Storwize V5000 does not support RAID 0.
- Number of volumes
- Expose to all hosts
  Note: The Expose to all hosts option can cause confusion in multisystem environments.
- LUN assignments

You can also modify, expand, or delete a volume by using either the SMU or the CLI.

Note: Before you delete the LUN on the MSA2000 system, use the rmdisk command to delete the MDisk on the Storwize V5000clustered system.

LUN presentation

You can also use the SMU or the CLI to map and unmap MSA2000 LUNs.

To map a logical unit (or volume), from the SMU complete these steps:

In the Storage Management Utility SMU interface, go to Manage > Volume Management > VDisk or Volume > Volume Mapping.
Under the section Assign Host Access Privileges, select Map Host to Volume.
For each Storwize V5000 WWPN, select SVC WWPN in the HOST WWN-Name menu.
Enter the LUN number to present to the Storwize V5000. For example, use 0 for the first volume, then use 1 for the second, until all volumes are assigned.
Select read-write for the Port 0 Access and Port 1 Access.
Click Map it. The resulting mapping is displayed in the Current Host-Volume Relationships section.
Important: Use the Current Host-Volume Relationships section to verify that the LUN ID is consistent and all Storwize V5000 WWPNs are mapped.

Because the following example is for an 8-node cluster, 32 WWPNs show in the show volume-maps output (four ports per node).

example shown for an 8-node cluster, that is, 32 WWPNs;
# show volume-maps
Volume [SN 00c0ffd76a330000a0fa124a01000000, Name (VD0_V1)] mapping view:
CH       ID LUN Access Host-Port-Identifier                    Nickname
-------------------------------------------------------------------------------
0,1       0   0 rw     50050768012FFFFF
0,1       0   0 rw     5005076801105CEE
0,1       0   0 rw     500507680110008A
0,1       0   0 rw     50050768011FFFFF
0,1       0   0 rw     50050768013FFFFF
0,1       0   0 rw     50050768014FFFFF
0,1       0   0 rw     500507680140008A
0,1       0   0 rw     500507680130008A
0,1       0   0 rw     500507680120008A
0,1       0   0 rw     5005076801405CEE
0,1       0   0 rw     5005076801205CEE
0,1       0   0 rw     5005076801305CEE
0,1       0   0 rw     500507680110596B
0,1       0   0 rw     5005076801305FB8
0,1       0   0 rw     5005076801205FB8
0,1       0   0 rw     5005076801405FB8
0,1       0   0 rw     5005076801105FB8
0,1       0   0 rw     500507680120596B
0,1       0   0 rw     500507680140596B
0,1       0   0 rw     500507680130596B
0,1       0   0 rw     5005076801400009
0,1       0   0 rw     5005076801300009
0,1       0   0 rw     5005076801100009
0,1       0   0 rw     5005076801200009
0,1       0   0 rw     50050768014FFFFE
0,1       0   0 rw     50050768013FFFFE
0,1       0   0 rw     50050768012FFFFE
0,1       0   0 rw     50050768011FFFFE
0,1       0   0 rw     5005076801200001
0,1       0   0 rw     5005076801400001
0,1       0   0 rw     5005076801300001
0,1       0   0 rw     5005076801100001

Note: LUNs from controller module A and controller module B can have the same LUN IDs (0). Controller module A and Controller module B appear on the Storwize V5000 system as separate controllers. Place managed disks (MDisks) on the system in separate storage pools so that each controller module has its own separate storage pool for its presented MDisks.

Special LUNs

Volumes can have a LUN ID in the range 0 - 126 on each controller. LUN 0 on the MSA2000 is visible from both controllers, but can be used only to access storage from the preferred controller. LUN 0 on the other controller does not present storage.

Target ports on MSA2000 systems

The MSA2000 system has two dual-active controllers with two ports each. You must set these ports as point-to-point by using the SMU interface.

In the Storage Management Utility SMU interface, go to Manage > General Config > Host Port Configuration. Select Advanced Options and specify point to point for Change Host Topology.

Each WWPN is identified with the pattern 2P:7N:CC:CC:CC:MM:MM:MM where P is the port number on the controller and N is the address of the controller port (0 or 8), CC:CC:CC represents the Organizationally Unique Identifier (OUI), and MM:MM:MM is unique for the particular controller.

example;
# show port-wwn
CTRL CH WWPN
-------------------------
A    0  207000C0FFD75198
A    1  217000C0FFD75198
B    0  207800C0FFD75198
B    1  217800C0FFD75198

LU access model

The MSA2000 is a dual-active system. Each LUN has an owning controller, and I/O is serviced only by ports on that controller. Failover automatically takes place when one controller fails (shuts down). Storwize V5000 cannot force failover.

LU grouping

The MSA2000 system does not support LU grouping.

LU preferred access port

The MSA system has two ports per controller. The I/O is through port 0, and port 1 is linked to port 0 of the other controller during a failure or a code upgrade.

Detecting ownership

The LUN is reported only by the target ports of the owning controller.

Failover

The only way to cause failover of LUs from one controller to the other is to shut down one of the controllers. The MSA2000 system cannot normally present all the system LUNs through both controllers. Therefore, it requires a four-port connection to two SAN fabrics. Failover for MS2000 systems involves the surviving controller taking its ports offline, then returning with one of its ports, emulating the WWPNs of the failed controller.

Note: This behavior also means that half of the operational paths from the surviving controller are taken away when failover takes place, which allows the port from the controller that is shutting down to be emulated.