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Channels

Dell OpenManage™ Storage Management User's Guide

Channel Redundancy on PERC 3/DCL, 3/DC, 3/QC, 4/DC, 4e/DC, 4/Di, and 4e/Di Controllers

Creating a Channel-redundant Virtual Disk

A controller contains one or more channels to which you can attach disks. A channel is externally accessible for attaching an enclosure (with external disks) to the system. A channel may also be attached to the system's backplane (for internal disks). The controller's channels are displayed by expanding the controller object in the tree view.

Channel Redundancy and Thermal Shutdown

It is possible to create a virtual disk that uses array disks that are attached to different controller channels. The array disks may reside in an external enclosure or the backplane (internal enclosure). If the virtual disk is maintaining redundant data on different channels, then the virtual disk is channel redundant. Channel redundancy means that if one of the channels fails, data will not be lost because redundant data resides on another channel.

Channel redundancy might also be used for disks that reside in enclosures subject to thermal shutdown. Should the enclosure attached to one of the channels shut down, redundant data is maintained on the other channel.

Channel redundancy is implemented by selecting array disks on different channels when using the Create Virtual Disk Advanced Wizard.

Note: Channel redundancy only applies to controllers that have more than one channel and that attach to an external disk enclosure.

If you wish to create a channel-redundant virtual disk, see the following sections:

Channel Redundancy on PERC 3/DCL, 3/DC, 3/QC, 4/DC, 4e/DC, 4/Di, and 4e/Di Controllers

The following considerations apply when creating a channel-redundant virtual disk on these controllers:

It is recommended that you use a RAID 10 or RAID 50 when implementing channel redundancy on the PERC 2/DC, 3/DCL, 3/DC, 3/QC, 4/DC, 4e/DC, 4/Di, and 4e/Di controllers.
If one of the channels (or enclosure) fails, you will no longer be able to maintain I/O operations on any of the channels included in the channel redundant configuration even though data has not been lost. To restore I/O, do one of the following:

Fix the failed channel and reboot the system.
Reboot the system. This will restore I/O on the channels that have not suffered a failure. The virtual disks on these channels will be in a degraded state.

Creating a Channel-redundant Virtual Disk

The following instructions describe creating a virtual disk that uses channel redundancy.

Note: Channel redundancy only applies to controllers that have more than one channel and that attach to an external disk enclosure.

Launch the Create Virtual Disk Advanced Wizard by doing the following:

Locate the controller on which you are creating a channel-redundant virtual disk Expand the Controller object until the Virtual Disk object is displayed.

Select the Virtual Disk object and click Go To Create Virtual Disk Wizard.

Click Virtual Disk Advanced Wizard.

Complete Create Virtual Disk Advanced Wizard (Step 1 of 4). This portion of the Create Virtual Disk Advanced Wizard asks you to select a RAID level. When creating a channel-redundant virtual disk, it is recommended that you select the following RAID levels.

Recommended RAID Levels:

PERC 3/DCL, 3/DC, 3/QC, 4/DC, 4e/DC, 4/Di, and 4e/Di Controllers: It is recommended that you only use RAID 10 or RAID 50.
PERC 2 and 3/Di Controllers: It is recommended that you only use RAID 10 or RAID 1-concatenated.

Complete Create Virtual Disk Advanced Wizard (Step 2 of 4). In this step, you select the channels and the disks to be used by the virtual disk. The selections you make determine whether or not the virtual disk is channel-redundant.

There are specific RAID level and configuration requirements for implementing channel redundancy. You must select the same number of array disks on each channel that you use. Refer to the "Number of Array Disks per Virtual Disk" section for information on the number of array disks that can be used for different RAID levels. Refer to the Controller-supported RAID Levels section for information on controller-specific implementations of the RAID levels.

Depending on the controller type, use one of the following procedures when completing Create Virtual Disk Advanced Wizard (Step 2 of 4):

Array Disk Selection for Channel-redundant Virtual Disks on PERC 3/DCL, 3/DC, 3/QC, 4/DC, 4e/DC, 4/Di, and 4e/Di Controllers

The following sections describe creating a channel-redundant virtual disk using RAID 10 or RAID 50 on a PERC 3/DCL, 3/DC, 3/QC, 4/DC, 4e/DC, 4/Di, or 4e/Di, controller.

RAID 10

Select one array disk on each of two channels. (In other words, each of the two channels will have a single disk selected.)

Select an additional disk on each of the two channels. You have now selected the minimum number of disks for a RAID 10.

Repeat step b until you have the desired number of disks.

Click Continue.

RAID 50

Select one array disk on each of three channels. (In other words, each of the three channels will have a single disk selected.)

Select an additional disk on each of the three channels. You have now selected the minimum number of disks for a RAID 50. Continue selecting a disk on each channel until you have selected the desired number of disks.

Repeat step b until you have the desired number of disks.

Click Continue.

Array Disk Selection for Channel-redundant Virtual Disks on PERC 2 and 3/Di Controllers:

The following section describes creating a channel-redundant virtual disk using RAID 10 or Concatenation of RAID 1 on a PERC 2 or 3/Di controller.

RAID 10 or Concatenation of RAID 1

Select one array disk on each of two channels. (In other words, each of the two channels will have a single disk selected.)

Select an additional disk on each of the two channels. You have now selected the minimum number of disks for a RAID 10 or Concatenation of RAID 1.

Repeat step b until you have selected the desired number of disks. You must select the same number of array disks on each channel that you use.

Click Continue.

Channel Health

This screen displays the status of the channel and the components attached to the channel.

Channel Status

Component status is indicated by the severity. A component with a Warning or Critical/Failure status requires immediate attention to avoid data loss if possible. It may be useful to review the Alert Log for events indicating why a component has a Warning or Critical status. For additional troubleshooting information, see Alert Messages and Troubleshooting.

The component status displayed on this screen reflects the status at a given point in time. If you believe the status has changed and wish to update this screen, select the controller's Information/Configuration tab and execute the Rescan task.

Severity

Component Status

Normal/OK. The component is working as expected.

Warning/Non-critical. A probe or other monitoring device has detected a reading for the component that is above or below the acceptable level. The component may still be functioning, but it could fail. The component may also be functioning in an impaired state. Data loss is possible.

Critical/Failure/Error. The component has either failed or failure is imminent. The component requires immediate attention and may need to be replaced. Data loss may have occurred.

Severity	Component Status
	Normal/OK. The component is working as expected.
	Warning/Non-critical. A probe or other monitoring device has detected a reading for the component that is above or below the acceptable level. The component may still be functioning, but it could fail. The component may also be functioning in an impaired state. Data loss is possible.
	Critical/Failure/Error. The component has either failed or failure is imminent. The component requires immediate attention and may need to be replaced. Data loss may have occurred.

Channel Information

For information on the channel, see the following topics:

Channel Components

For information on attached components, see the following topics:

Enclosures and Backplanes

Channel Properties and Tasks

Use this window to view information about the channel and execute channel tasks.

Channel Properties

The channel properties can vary depending on the model of the controller. Channel properties may include:

Property

Definition

These icons represent the severity or health of the storage component. See Storage Component Severity for more information.

Name
This property displays the channel number.

State
This property displays the current status of the channel. Possible values are:
Ready — The channel is functioning normally.

Degraded — The channel has suffered a failure of a component and is operating in a degraded state.

Failed — The channel has suffered a failure of one or more components and is no longer functioning.

Termination
This property displays the size of the controller channel. Possible values are:
Narrow — Indicates an 8 bit channel.

Wide — Indicates a 16 bit channel.

SCSI Rate
This property displays the SCSI speed.

Property	Definition
	These icons represent the severity or health of the storage component. See Storage Component Severity for more information.
Name	This property displays the channel number.
State	This property displays the current status of the channel. Possible values are: Ready — The channel is functioning normally. Degraded — The channel has suffered a failure of a component and is operating in a degraded state. Failed — The channel has suffered a failure of one or more components and is no longer functioning.
Termination	This property displays the size of the controller channel. Possible values are: Narrow — Indicates an 8 bit channel. Wide — Indicates a 16 bit channel.
SCSI Rate	This property displays the SCSI speed.

Channel Tasks: Rescan Channel

This task rescans the controller channels to verify the currently connected devices or to recognize new devices that have been added to the channels. Performing a rescan on a channel is similar to performing a rescan on the controller. For information on when you may want to do a rescan, see Rescan to Update Storage Configuration Changes.

On non-RAID SCSI controllers, the operating system must be able to see any hardware changes before initiating the controller rescan. Otherwise, the hardware changes may not be reflected in the Storage Management graphical user interface (GUI). Refer to the operating system documentation for information on updating hardware changes. You can also reboot the system to update hardware changes with the operating system.

Do the following to rescan a controller channel:

Expand the Storage tree object to display the controller objects.
Expand a controller object.
Select a channel object.
Select the Information/Configuration subtab.
Select Rescan from the Available Tasks drop-down menu.
Click Execute.

Channel Components

For information on attached components, see the following topics:

Enclosure and Backplane Properties and Tasks

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