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Description of problem: This value hangs around in a device's udev properties even when device is no longer multipathed. Other DM_MULTIPATH_* values disappear. Version-Release number of selected component (if applicable): Name : device-mapper-multipath Arch : x86_64 Version : 0.4.9 Release : 85.el7 Size : 178 k Repo : installed From repo : RHEL-7 How reproducible: Seems consistent. Steps to Reproduce: 1. Remove some multipath devices from a group. 2. Use udevadm to list their udev properties. 3. Notice that DM_MULTIPATH_TIMESTAMP remains even while other DM_MULTIPATH_* properties are gone. Actual results: DM_MULTIPATH_TIMESTAMP remains, other DM_MULTIPATH_* properties gone. Expected results: I was a little surprised to see any DM_MULTIPATH_* properties remaining for the device. Additional info: This may be quite deliberate, but even a reboot doesn't seem to clear it.
DM_MULTIPATH_TIMESTAMP will always be there when multipathing is enabled and multipathd is running. It's purpose it to cut down on how often multipath has to check if a device is a multipath path. This can take a bit of time, so we don't want to check on every change event. Instead, multipathd updates a timestamp whenever a new path device is discovered for the first time, or the configuration file is reloaded. When a change event happens, the device checks its existing timestamp value against the current one, and if it has changed, multipath will recheck the path.