SAN Boot Implementation and Best Practices Guide ... - IBM Redbooks

SG247958-iSCSI_DS5000-CL.fm Draft Document for Review June 27, 2012 9:05 am
multipath –ll output does not show all the LUNs.
This most probably is because Device Mapper is not seeing all the LUNs mapped to it. This
can happen due to various reasons,
If mappings are edited with the host connected to the array. The host in some case might fail
to monitor for newly added LUNs and there will not be a scsi block device created for these
newly added LUNs. To fix this issue rescan for the scsi devices using the command
“rescan_scsi_bus”. This should create scsi device for the newly added LUNs and run
“multipath” to add the scsi devices to device mapper table.
multipath does not show paths equal to the number of LUNs mapped
The first thing that you should check is the ‘lsscsi’ output to see if the SCSI midlayer is seeing
(# of paths x # of LUNs) number of block devices.
If not issue a device rescan by “rescan-scsi-bus.sh”. This should fix the issue else reboot the
host.
If “lsscsi” is seeing all the devices, then do the following steps:
► Issue “multipath“ so that device mapper can add the devices seen by lsscsi
► Flush all the mappings and re-add them (multipath –F ; multipath)
► Restart multipath daemon (service multipathd restart)
multipath -ll output is showing the paths as [failed][faulty]
This could happen with the physical path to a controller fails or the controller itself fails and
failover happens.
► Verify the disk uid and parameters in multipath.conf file.
► Verify cables and zoning configuration.
► If this happens after an error in test and you want to make the configuration optimal, save
the logs first, then flush and re-add multipath devices, restart multipath daemon. If the
issue still persists, reboot the system.
6.6 More Information
As the support for iSCSI SAN Boot is increasing on IBM products, refer to the latest
interoperability information at the IBM website: System Storage Interoperation Center (SSIC),
at:
http://www-03.ibm.com/systems/support/storage/ssic/interoperability.wss
444 SAN Boot Implementation and Best Practices Guide for IBM System Storage