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Alternate Control Path in depth information

Can anyone point me to in depth information about this feature on the DS4243 Shelf.

The only thing i can find is, that it is delivering out of data path management and how it is turned on en cabled.

Is there another technical document about this feature?

Tomas

Re: Alternate Control Path in depth information

I don't think there is. We did a deep search the other week during a boot camp

and that's about all the information that could be found.

At your service,

Eugene Kashpureff

Re: Alternate Control Path in depth information

Tnx, glad to hear i am not the only one.

mmm lets try to find this trough another channel....

Re: Alternate Control Path in depth information

Here is what i foundon the now site

How Data ONTAP uses ACP to increase storage availability

ACP, or Alternate Control Path, is a protocol that enables Data ONTAP to manage and control the DS4243 disk shelf storage subsystem. It uses a separate network (alternate path) from the data path, so management communication is not dependent on the data path's being intact and available.

You do not need to actively manage the DS4243 storage subsystem. Data ONTAP automatically monitors and manages the subsystem without operator intervention. However, you must provide the required physical connectivity and configuration parameters to enable the ACP functionality.

Note: You can install DS4243 disk shelves without configuring ACP. However, for maximum storage availability and stability, you should always have ACP configured and enabled.

After you enable ACP, you can use the storage show acp and acpadmin list all commands to display information about your ACP subsystem.

  • Enabling ACP
    ACP (Alternative Control Path) can increase your storage availability when you use DS4243 disk shelves. To access the benefits, you must configure and enable ACP on your storage system.
  • The ACP subnet
    The ACP subnet is a private Ethernet network that enables the ACP processor in the SAS module to communicate both with Data ONTAP and with the SAS IOMs in the disk shelves. This network is separate from the I/O data path that connects the disk shelves to the HBA on the storage controller.


Enabling ACP

ACP (Alternative Control Path) can increase your storage availability when you use DS4243 disk shelves. To access the benefits, you must configure and enable ACP on your storage system.

1.1.1      Before you begin

ACP must be cabled before beginning this procedure. For more information, see the DS4243 System Connectivity flyer.

In addition, if you have not previously configured the network connectivity for ACP, you must assemble the following network configuration information for the ACP connection:

  • Network interface

The designated interface for ACP traffic

  • Domain for network interface

The network name (an IP address ending in 0) for the private subnet to be used exclusively by ACP (if you do not choose to use the default value)

  • Netmask for network interface

The network mask for the ACP subnet (if you do not choose to use the default value)

1.1.2      About this task

If, after you perform this task, you want to change the ACP configuration values later, you can use the setup command.

1.1.3      Step

  1. At the Data ONTAP command line, enter the following command:options acp.enabled on

If you have not previously configured the networking information for ACP, you are prompted for that information.

Parent topic: How Data ONTAP uses ACP to increase storage availability


The ACP subnet

The ACP subnet is a private Ethernet network that enables the ACP processor in the SAS module to communicate both with Data ONTAP and with the SAS IOMs in the disk shelves. This network is separate from the I/O data path that connects the disk shelves to the HBA on the storage controller.

When you configure ACP on one of the system's network interfaces, you must supply a private domain name that conforms to RFC1918. You can use the system default domain, 198.15.1.0, or another network name (that is, an IP address ending in 0) that conforms to RFC1918.

If you are configuring ACP for disk shelves attached to an active/active configuration, you must supply the same ACP domain name and network mask for both systems.

Attention: Do not connect the ACP port to a routed network, and do not configure switches or hubs between the ACP port and the designated Ethernet port. Doing so is not supported and will cause interruptions in service.

After you select a domain name and network mask for the interface, Data ONTAP automatically assigns IP addresses for traffic in the ACP subnet. This assignment also includes the storage controller network interface that you selected for ACP traffic.

For example, if you selected e0b as the interface for ACP traffic, you will see command output similar to the following:

my-sys-1> storage show acp

Alternate Control Path:  enabled

Ethernet Interface:      e0b

ACP Status:              Active

ACP IP address:          198.15.1.212

ACP domain:              198.15.1.0

ACP netmask:             255.255.255.0

ACP Connectivity Status: Partial Connectivity

Shelf Module      Reset Cnt    IP address      FW Version    Status

---------------------------------------------------------------------

7a.001.A          002          198.15.1.145    01.05         active

7a.001.B          003          198.15.1.146    01.05         active

7c.002.A          000          198.15.1.206    01.05         active

7c.002.B          001          198.15.1.204    01.05         active


Shelf Alternate Control Path Management information

If you are planning to attach DS4243 disk shelves to your system, you should configure Shelf Alternate Control Path Management (ACP) during the software setup process.

Note: ACP connections must be cabled before you enter ACP configuration parameters on the storage system.

You can also configure ACP by using one of the following methods after the initial setup process:

  • Running the Data ONTAP setup script

You can run the setup command and enter ACP configuration information.

  • Setting the acp.enabled option to on

If the option has not previously been set, you will be prompted for ACP configuration values.

For more information about ACP configuration, see the DS4243 Installation and Service Guide.

Information type

Description

Network interface name

The name of the Ethernet (or GbE) interface that will be used exclusively for ACP traffic.

Domain for network interface

The network name (an IP address ending in 0) for the private subnet to be used exclusively by ACP. The default is 198.15.1.0.

Netmask for network interface

The subnet mask for the ACP interface.

  • The ACP subnet
    The ACP subnet is a private Ethernet network that enables the ACP processor in the SAS module to communicate both with Data ONTAP and with the SAS IOMs in the disk shelves. This network is separate from the I/O data path that connects the disk shelves to the HBA on the storage controller.


Updating ACP firmware

If your disk shelves include Shelf Alternate Control Path Management (ACP) functionality, you can update ACP firmware by running the storage download acp command after downloading new ACP processor firmware from the NOW site.

1.1.4      Before you begin

ACP interfaces must be cabled properly and ACP software must be configured correctly. For more information, see the DS4243 Installation and Service Guide and the Data ONTAP 8.0 7-Mode Storage Management Guide.

1.1.5      About this task

When you upgrade Data ONTAP, ACP firmware (firmware for ACP processors on disk shelves) is updated automatically if the firmware in the ACP processors is older than the firmware that is bundled with the Data ONTAP system files. However, it might be necessary to update ACP firmware by downloading the most recent firmware from the NOW site and installing the files.

Note: Installing ACP firmware can take several minutes, but it will not disrupt client access during that time. However, normal ACP recovery capabilities will not be available while the firmware upgrade is in progress.

1.1.6      Steps

  1. Find and download the most recent ACP firmware on the NOW site.
  2. Follow the instructions on the NOW site to extract your firmware files to the /etc/acpp_fw directory in the root volume of your storage system.
  3. Enter the following command to update the ACP firmware:storage download acp

For more information about the command, see the storage(1) man page.

  1. Enter the following command to verify the new ACP firmware: storage show acp

You should see command output similar to the following while the ACP firmware is being updated:

Alternate Control Path:  enabled
Ethernet Interface:      e0b
ACP Status:              Active
ACP IP address:          198.15.1.212
ACP domain:              198.15.1.0
ACP netmask:             255.255.255.0
ACP Connectivity Status: Full Connectivity
Shelf Module      Reset Cnt    IP address      FW Version    Status
---------------------------------------------------------------------
7a.001.A          001          198.15.1.145    1.01           inactive (upgrading firmware)
7a.001.B          000          198.15.1.146    1.1           active
7c.002.A          000          198.15.1.206    1.1           active
7c.002.B          000          198.15.1.204    1.1           active

When the update has completed, you will see output similar to the following when you reissue the command:

Shelf Module      Reset Cnt    IP address      FW Version    Status
---------------------------------------------------------------------
7a.001.A          001          198.15.1.145    1.2           active
7a.001.B          000          198.15.1.146    1.1           active
7c.002.A          000          198.15.1.206    1.1           active
7c.002.B          000          198.15.1.204    1.1           active


Verifying ACP connections

If DS4243 disk shelves are connected to your system, use this procedure to verify that Shelf Alternate Control Path Management (ACP) is set up correctly and connected to a local LAN.

1.1.7      About this task

For more information about using ACP to increase storage availability, see your Data ONTAP Storage Management Guide.

1.1.8      Step

  1. To verify that ACP is enabled, enter the following command: storage show acp

You should see command output similar to the following:

Alternate Control Path:  enabled
Ethernet Interface:      e0b
ACP Status:              Active
ACP IP address:          198.15.1.212
ACP domain:              198.15.1.0
ACP netmask:             255.255.255.0
ACP Connectivity Status: Full Connectivity
Shelf Module      Reset Cnt    IP address      FW Version    Status
---------------------------------------------------------------------
7a.001.A          002          198.15.1.145    01.05           active
7a.001.B          003          198.15.1.146    01.05           active
7c.002.A          000          198.15.1.206    01.05           active
7c.002.B          001          198.15.1.204    01.05           active

acpadmin list_all

Displays information about the ACP (Alternate Control Path) storage subsystem.

storage show acp

Displays information about the ACP (Alternate Control Path) storage subsystem.


The ifconfig command and the FAS2040 e0P port

Do not use the ifconfig command to configure the e0P port on a FAS2040 system. This port is used to implement the Disk Shelf Alternate Control Path network only and is configured automatically.

Re: Alternate Control Path in depth information

That's about all we found for documentation as well.

My guess on the 'management communication' information that's being transmitted is that it's environmental and disk performance related, but that's just a guess...

At your service,

Eugene Kashpureff

Re: Alternate Control Path in depth information

Hello all,

To summarize what ACP (Alternate Control Path) is ...

ACP is recommended, but not required.  In the current implementation ACP does a couple of things (when enabled and cabled properly):

  • It continuosly compares the shelf modules that it can see on the ACP network to the shelf modules visible on the data path.  This can help you identify when there are problems with connectivity on the data path (when ACP can see a module that is not seen on the data path --- ACP status will indicate this by reporting "Additional Connectivity" in the output of the sysconfig command).
  • It enables Data ONTAP's proactive self recovery.  This is delivered over the ACP network (independant of the data path) --- if a situation is identified that would require either a SAS expander reset or power cycle Data ONTAP will automatically discover this need and execute the appropriate action (reset or power cycle of the expander) to resolve the issue.  This error recovery is delivered nondisruptively.  Users can manually execute SAS expander resets and power cycles (if ACP is disabled) --- but this would have to been done manually after identifying the issue manually (ACP does all this for you automatically).

ACP connectivity is reported as one of the following (in the sysconfig command output):

  • No Connectivity” – no ACP connected.
  • Full Connectivity” – data path matches control path (ACP network).
  • Partial Connectivity” – some IOMs seen only on data path (not on the ACP network).
  • Additional Connectivity” – some IOMs seen only on ACP (not on data path).
  • NA” - Not applicable where ACP is disabled.

Systems wishing to use ACP should be running Data ONTAP 7.3.3P2 or later, or 8.0P1 or later.

Regards,

Jay White

TME - Storage and RAID

NetApp