DELL MD3220 사용자 설명서

Configuration: Device Mapper Multipath for Linux

• In certain error conditions with the no_path_retry or the 

queue_if_no_path feature is set, applications may hang. To overcome 

these conditions the you must enter the following command for each 

affected multipath device: 
dmsetup message [device] 0 "fail_if_no_path" 
where [device] is the multipath device name (for example. mpath2; do 

not specify the path)

• I/O may hang when a Device Mapper device is deleted before the volume 

is unmounted.

• If the scsi_dh_rdac module is not included in initrd, slower device 

discovery may be seen and the syslog may become populated with buffer 

I/O error messages.

• I/O may hang if the host server or storage array is rebooted while I/O is 

active. All I/O to the storage array should be stopped before shutting down 

or rebooting the host server or storage array.

• With the MD3200 Series array, after a failed path is restored, failback does 

not automatically occur because the driver cannot auto-detect devices 

without a forced rescan. Run the command rescan_dm_devs to force a 

rescan of the host server. This restores the failed paths enabling failback to 

occur.

• Failback can be slow when the host system is experiencing heavy I/O. The 

problem is exacerbated if the host server is also experiencing very high 

CPU utilization.

• The Device Mapper Multipath service can be slow when the host system is 

experiencing heavy I/O. The problem is exacerbated if the host server also 

experiences very high CPU utilization.

• If the root disk is not blacklisted in the multipath.conf file, a multipathing 

node may be created for the root disk. The command multipath –ll 

lists vendor/product ID which can help identify this issue. 

book.book  Page 174  Monday, June 21, 2010  11:00 AM