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System Administration Guide: Devices and File Systems
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Dynamic Reconfiguration and Hot-Plugging

Hot-plugging is the ability to physically add, remove, or replace system components while the system is running. Dynamic reconfiguration refers to the ability to hot-plug system components. This term also refers to the general ability to move system resources (both hardware and software) around in the system or to disable them in some way without physically removing them from the system.

Generally, you can hot-plug the following bus types:

  • USB

  • Fibre Channel

  • 1394

  • ATA

  • SCSI

In addition, you can hot-plug the following devices with the cfgadm command:

  • USB devices on SPARC and x86 platforms

  • SCSI devices on SPARC and x86 platforms

  • PCI devices on SPARC and x86 platforms

  • PCIe devices on SPARC or x86 platforms

Features of the cfgadm command include the following:

  • Displaying system component status

  • Testing system components

  • Changing component configurations

  • Displaying configuration help messages

The benefit of using the cfgadm command to reconfigure systems components is that you can add, remove, or replace components while the system is running. An added benefit is that the cfgadm command guides you through the steps needed to add, remove, or replace system components.

For step-by-step instructions on hot-plugging components, see the following:

Note - Not all SCSI and PCI controllers support hot-plugging with the cfgadm command.

As part of Sun's high availability strategy, dynamic reconfiguration is expected to be used in conjunction with additional layered products, such as alternate pathing or fail over software. Both products provide fault tolerance in the event of a device failure.

Without any high availability software, you can replace a failed device by manually stopping the appropriate applications, unmounting noncritical file systems, and then proceeding with the add or remove operations.

Note - Some systems have slots that hot-pluggable and slots that are not hot-pluggable. For information about hot-plugging devices on your specific hardware configuration, such as on enterprise-level systems, refer to your hardware configuration documentation.

Attachment Points

The cfgadm command displays information about attachment points, which are locations in the system where dynamic reconfiguration operations can occur.

An attachment point consists of the following:

  • An occupant, which represents a hardware component that can be configured into the system

  • A receptacle, which is the location that accepts the occupant

Attachment points are represented by logical and physical attachment point IDs (Ap_Ids). The physical Ap_Id is the physical path name of the attachment point. The logical Ap_Id is a user-friendly alternative for the physical Ap_Id. For more information on Ap_Ids, refer to cfgadm(1M).

The logical Ap_Id for a SCSI Host Bus Adapter (HBA), or SCSI controller, is usually represented by the controller number, such as c0.

In cases where no controller number has been assigned to a SCSI HBA, then an internally generated unique identifier is provided. An example of a unique identifier for a SCSI controller is the following:


The logical Ap_Id for a SCSI device usually has this format:


In the following example, c0 is the logical Ap_Id for the SCSI HBA:


The device identifier is typically derived from the logical device name for the device in the /dev directory. For example, a tape device with logical device name, /dev/rmt/1, has the following logical Ap_Id:


If a logical Ap_Id of a SCSI device cannot be derived from the logical name in the /dev directory, then an internally generated unique identifier is provided. An example of an identifier for the /dev/rmt/1 tape device is the following:


For more information on SCSI Ap_Ids, refer to cfgadm_scsi(1M).

The cfgadm command represents all resources and dynamic reconfiguration operations in terms of a common set of states (such as configured and unconfigured) and operations (such as connect, configure, unconfigure, and so on). For more information on these common states and operations, see cfgadm(1M).

The following table shows the receptacle and occupant states for the SCSI HBA attachment points.

Receptacle State


Occupant State





One or more devices is configured on the bus


Bus quiesced


No devices are configured


Bus active

The following table shows the receptacle and occupant states for SCSI device attachment points.

Receptacle State


Occupant State



N/A for SCSI devices


Device is configured


Bus quiesced


Device is not configured


Bus active

The state of SCSI attachment points is unknown unless special hardware indicates otherwise. For instructions on displaying SCSI component information, see How to Display Information About SCSI Devices.

Detaching PCI or PCIe Adapter Cards

A PCI adapter card that is hosting nonvital system resources can be removed if the device driver supports hot-plugging. A PCI adapter card is not detachable if it is a vital system resource. For a PCI adapter card to be detachable, the following conditions must be met:

  • The device driver must support hot-plugging.

  • Critical resources must be accessible through an alternate pathway.

For example, if a system has only one Ethernet card installed in it, the Ethernet card cannot be detached without losing the network connection. This detachment requires additional layered software support to keep the network connection active.

Attaching PCI or PCIe Adapter Cards

A PCI adapter card can be added to the system as long as the following conditions are met:

  • There are slots available.

  • The device driver supports hot-plugging for this adapter card.

For step-by-step instructions on adding or removing a PCI adapter card, see PCI or PCIe Hot-Plugging With the cfgadm Command.

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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire