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Operating Systems Linux Red Hat Device Mapper Notations and LVM Post 302378000 by mark54g on Sunday 6th of December 2009 10:11:27 AM
Old 12-06-2009
When using SCSI devices, the path is clearly defined based on the SCSI ID of the controller, the port that the device is connected to, etc.

SATA/SAS drives do not have this luxury, as they are not defined on a chain. This causes some confusion, as when /dev/sda comes up next time, it may be /dev/sdc.

dev-mapper uses a different, non-volatile ID such as UUID or disk label (contained in metadata) to keep disk paths consistent, through its abstraction.

Basically, the short version is:

To make sure that your devices are named and in a consistent path, dev-mapper handles the devices so that your / is found properly each bootup and is not confused with /tmp or some other file system on another device.
 

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DMEVENT_TOOL(8) 														   DMEVENT_TOOL(8)

NAME
dmevent_tool - A utility used to load a DSO into dmeventd and (un)register devices with it for monitoring SYNOPSIS
dmevent_tool -[Vhmru] {RAID device name} {DSO Name} DESCRIPTION
dmevent_tool is a userspace utility used to register/unregister DSOs with the daemon dmeventd. If used with the -m command line parameter users can display all of the actively dmeventd monitored devices. OPTIONS
-V Show version of dmevent_tool -{h/?} Show this help information -m[r|u] List all currently active device mapper devices and their current status with dmeventd for registered (-r)/unregistered (-m) devices Syntax: dmevent_tool -m[u|r] -a[r|u] Same as -m, but for devices with UUID only! Syntax: dmevent_tool -a[u|r] -r Register a device with dmeventd Syntax: dmevent_tool -r <device name> <path to DSO library> Example: dmevent_tool -r isw_abcdeh_Volume0 libdmraid-events.so -u Unregister a device with dmeventd Syntax: dmevent_tool -u <device name> [<path to DSO library>] Example: dmevent_tool -u isw_abcdefgh_Volume0 EXAMPLES
dmevent_tool -m is used to display all of the actively monitored devices dmevent_tool -m Device Name: isw_defeaigdde_Volume0_dmraid00 Registered DSO: libdmraid-events.so UUID: isw_defeaigdde_Volume0_dmraid00 status: Active major device #: 253 minor device #: 0 read only device: No number of recorded kernel events: 0 SATA drives in this volume group: /dev/sdb /dev/sdc dmevent_tool -r is used to register a volume group device with dmeventd dmevent_tool -r isw_defeaigdde_Volume0_dmraid00 libdmraid-events.so dmevent_tool -u is used to unregister a volume group from dmeventd dmevent_tool -u isw_defeaigdde_Volume0_dmraid00 DIAGNOSTICS
dmevent_tool returns an exit code of 0 for success or 1 for error. AUTHOR
Brian Wood <brian.j.wood@intel.com> Brian Wood 1.0.0.rc3 DMEVENT_TOOL(8)
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