The device-mapper-multipath packages provide tools to manage multipath devices using the device-mapper multipath kernel module.
By default, the
multipathd service starts up before the
iscsi service. This provides multipathing support early in the bootup process and is necessary for multipathed iSCSI SAN boot setups. However, once started, the
multipathd service adds paths as informed about them by udev. As soon as the
multipathd service detects a path that belongs to a multipath device, it creates the device. If the first path that multipathd notices is a passive path, it attempts to make that path active. If it later adds a more optimal path,
multipathd activates the more optimal path. In some cases, this can cause a significant overhead during a startup.
If you are experiencing such performance problems, define the
service to start after the
service. This does not apply to systems where the root device is a multipathed iSCSI device, since it the system would become unbootable. To move the service start time run the following commands:
mv /etc/rc5.d/S06multipathd /etc/rc5.d/S14multipathd
mv /etc/rc3.d/S06multipathd /etc/rc3.d/S14multipathd
To restore the original start time, run the following command:
chkconfig multipathd resetpriorities
multipath command with the
-ll option can cause the command to hang if one of the paths is on a blocking device. Note that the driver does not fail a request after some time if the device does not respond.
This is caused by the cleanup code, which waits until the path checker request either completes or fails. To display the current
state without hanging the command, use