Assigned CMs
A controller that controls access is assigned to each RAID group and manages the load balance in the ETERNUS DX. The controller that controls a RAID group is called an assigned CM.
For the RAID group assigned CMs and drives for configuring the RAID group, there are no issues configuring them under different controller enclosures.
If specific controllers have a load bias, change the assigned CM to equalize the load. For more details, refer to "Change Controlling CM" in "Web GUI User's Guide".
If an assigned controller is disconnected for any reason, the assigned CM is replaced by another controller. After the disconnected controller is installed again and returns to normal status, this controller becomes the assigned CM again.
Auto Assignment of Assigned CMs
This section describes the selection criteria if auto assignment is selected for an assigned CM when RAID groups are created. It is also possible to manually change the assigned CM.
The assigned CM is determined by the value when the RAID group number is divided by the number of controllers. If a CM exists that is not installed or is malfunctioning, the assigned CM is allocated such that the load is evenly distributed across the CMs that are running normally.
The following table shows the assigned CM when all CMs are installed and are running normally.
The value when the RAID group number is divided by the number of controllers |
Assigned CMs (auto assignment) |
|---|---|
Even number |
CE#0 CM#0 |
Odd number |
CE#0 CM#1 |
The remainder when the RAID group number is divided by the number of controllers |
Number of CMs (number of CEs) |
|
|---|---|---|
2 (1CE) |
4 (2CE) |
|
0 |
CE#0 CM#0 |
CE#0 CM#0 |
1 |
CE#0 CM#1 |
CE#1 CM#1 |
2 |
— |
CE#1 CM#0 |
3 |
— |
CE#0 CM#1 |
The value of the remainder when the RAID group number is divided by the number of controllers |
Assigned CMs (auto assignment) |
Controller enclosure number (n) |
|---|---|---|
The value of the remainder is an even number |
CM#0 in controller enclosure #n |
n = value of the remainder ¸ 2 |
The value of the remainder is an odd number |
CM#1 in controller enclosure #n |
n = the number of controller enclosures — (value of the remainder + 1) ¸ 2 |
An example of auto assignment of assigned CMs is shown below.
Example 1
When creating a RAID group where the RAID group No. is 30 in a single controller enclosure configuration (with two controllers)
The value of the remainder when the RAID group number is divided by the number of controllers
30 ¸ 2 = 15 and the remainder is 0
Controller enclosure number
0
The assigned CM is CM#0 in controller enclosure #0.
Example 2
When creating a RAID group where the RAID group No. is 31 in a 12-controller-enclosure configuration (with 24 controllers)
The value of the remainder when the RAID group number is divided by the number of controllers
31 ¸ 24 = 1 and the remainder is 7
Controller enclosure number
12 - (7 + 1) ¸ 2 = 8
The assigned CM is CM#1 in controller enclosure #8.
For more details about the auto assignment of assigned CM, refer to "Web GUI User's Guide".