Dynamic Multi-Pathing 7.3.1 Administrator's Guide - Linux
- Understanding DMP
- Setting up DMP to manage native devices
- About setting up DMP to manage native devices
- Displaying the native multi-pathing configuration
- Migrating LVM volume groups to DMP
- Migrating to DMP from EMC PowerPath
- Migrating to DMP from Hitachi Data Link Manager (HDLM)
- Migrating to DMP from Linux Device Mapper Multipath
- Using Dynamic Multi-Pathing (DMP) devices with Oracle Automatic Storage Management (ASM)
- Enabling Dynamic Multi-Pathing (DMP) devices for use with Oracle Automatic Storage Management (ASM)
- Removing Dynamic Multi-Pathing (DMP) devices from the listing of Oracle Automatic Storage Management (ASM) disks
- Migrating Oracle Automatic Storage Management (ASM) disk groups on operating system devices to Dynamic Multi-Pathing (DMP) devices
- Adding DMP devices to an existing LVM volume group or creating a new LVM volume group
- Removing DMP support for native devices
- Administering DMP
- About enabling and disabling I/O for controllers and storage processors
- About displaying DMP database information
- Displaying the paths to a disk
- Setting customized names for DMP nodes
- Administering DMP using the vxdmpadm utility
- Retrieving information about a DMP node
- Displaying consolidated information about the DMP nodes
- Displaying the members of a LUN group
- Displaying paths controlled by a DMP node, controller, enclosure, or array port
- Displaying information about controllers
- Displaying information about enclosures
- Displaying information about array ports
- User-friendly CLI outputs for ALUA arrays
- Displaying information about devices controlled by third-party drivers
- Displaying extended device attributes
- Suppressing or including devices from VxVM control
- Gathering and displaying I/O statistics
- Setting the attributes of the paths to an enclosure
- Displaying the redundancy level of a device or enclosure
- Specifying the minimum number of active paths
- Displaying the I/O policy
- Specifying the I/O policy
- Disabling I/O for paths, controllers, array ports, or DMP nodes
- Enabling I/O for paths, controllers, array ports, or DMP nodes
- Renaming an enclosure
- Configuring the response to I/O failures
- Configuring the I/O throttling mechanism
- Configuring Subpaths Failover Groups (SFG)
- Configuring Low Impact Path Probing (LIPP)
- Displaying recovery option values
- Configuring DMP path restoration policies
- Stopping the DMP path restoration thread
- Displaying the status of the DMP path restoration thread
- Configuring Array Policy Modules
- Administering disks
- About disk management
- Discovering and configuring newly added disk devices
- Partial device discovery
- About discovering disks and dynamically adding disk arrays
- About third-party driver coexistence
- How to administer the Device Discovery Layer
- Listing all the devices including iSCSI
- Listing all the Host Bus Adapters including iSCSI
- Listing the ports configured on a Host Bus Adapter
- Listing the targets configured from a Host Bus Adapter or a port
- Listing the devices configured from a Host Bus Adapter and target
- Getting or setting the iSCSI operational parameters
- Listing all supported disk arrays
- Excluding support for a disk array library
- Re-including support for an excluded disk array library
- Listing excluded disk arrays
- Listing disks claimed in the DISKS category
- Displaying details about an Array Support Library
- Adding unsupported disk arrays to the DISKS category
- Removing disks from the DISKS category
- Foreign devices
- Changing the disk device naming scheme
- Discovering the association between enclosure-based disk names and OS-based disk names
- Dynamic Reconfiguration of devices
- About online Dynamic Reconfiguration
- Reconfiguring a LUN online that is under DMP control using the Dynamic Reconfiguration tool
- Manually reconfiguring a LUN online that is under DMP control
- Overview of manually reconfiguring a LUN
- Manually removing LUNs dynamically from an existing target ID
- Manually adding new LUNs dynamically to a new target ID
- About detecting target ID reuse if the operating system device tree is not cleaned up
- Scanning an operating system device tree after adding or removing LUNs
- Manually cleaning up the operating system device tree after removing LUNs
- Changing the characteristics of a LUN from the array side
- Upgrading the array controller firmware online
- Reformatting NVMe devices manually
- Event monitoring
- Performance monitoring and tuning
- About tuning Dynamic Multi-Pathing (DMP) with templates
- DMP tuning templates
- Example DMP tuning template
- Tuning a DMP host with a configuration attribute template
- Managing the DMP configuration files
- Resetting the DMP tunable parameters and attributes to the default values
- DMP tunable parameters and attributes that are supported for templates
- DMP tunable parameters
- Appendix A. DMP troubleshooting
- Appendix B. Reference
How DMP monitors I/O on paths
In VxVM prior to release 5.0, DMP had one kernel daemon (errord) that performed error processing, and another (restored) that performed path restoration activities.
From release 5.0, DMP maintains a pool of kernel threads that are used to perform such tasks as error processing, path restoration, statistics collection, and SCSI request callbacks. The name restored has been retained for backward compatibility.
One kernel thread responds to I/O failures on a path by initiating a probe of the host bus adapter (HBA) that corresponds to the path. Another thread then takes the appropriate action according to the response from the HBA. The action taken can be to retry the I/O request on the path, or to fail the path and reschedule the I/O on an alternate path.
The restore kernel task is woken periodically (by default, every 5 minutes) to check the health of the paths, and to resume I/O on paths that have been restored. As some paths may suffer from intermittent failure, I/O is only resumed on a path if the path has remained healthy for a given period of time (by default, 5 minutes). DMP can be configured with different policies for checking the paths.
The statistics-gathering task records the start and end time of each I/O request, and the number of I/O failures and retries on each path. DMP can be configured to use this information to prevent the SCSI driver being flooded by I/O requests. This feature is known as I/O throttling.
If an I/O request relates to a mirrored volume, VxVM specifies the FAILFAST flag. In such cases, DMP does not retry failed I/O requests on the path, and instead marks the disks on that path as having failed.