Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE FOR EVMS Administration Manual

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Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE FOR EVMS Administration Manual Manual pdf 45 page image

Managing Multipath I/O for Devices 45novdocx (ENU) 9 January 2007See the vendor’s specific instructions for more details. After the driver module is loaded, discover the device nodes assigned to specific array LUNs orpartitions.If the LUNs are not seen by the HBA driver, lsscsi can be used to check whether the SCSIdevices are seen correctly by the operating system. When the LUNs are not seen by the HBA driver,check the zoning setup of the SAN. In particular, check whether LUN masking is active and whetherthe LUNs are correctly assigned to the server.If the LUNs are seen by the HBA driver, but there are no corresponding block devices, additionalkernel parameters are needed to change the SCSI device scanning behavior, such as to indicate thatLUNs are not numbered consecutively. For information, see Options for SCSI Device Scanning(http://www.novell.com/support/search.do?cmd=displayKC&docType=kc&externalId=http--supportnovellcom-techcenter-sdb-en-2005-06-drahnscsiscanninghtml&sliceId=) in the NovellTechnical Support Knowledgebase.5.2.2 Partitioning Devices that Have Multiple PathsPartitioning devices that have multiple paths is not recommended. However, if you want to partitionthe device, you should configure its partitions using fdisk or YaST2 before configuringmultipathing. This is necessary because partitioning a DM-MPIO device is not supported.Partitioning operations on md# devices fail if attempted.If you configure partitions for a device, DM-MPIO automatically recognizes the partitions andindicates them by appending p1-pn to the device’s UUID, such as/dev/disk/by-id/3600601607cf30e00184589a37a31d911p1To partition DM-MPIO devices, you must disable DM-MPIO, partition the normal device node(such as /dev/sdc), then reboot to allow DM-MPIO to see the new partitions.5.2.3 Configuring mdadm.conf and lvm.conf to Scan Devicesby UUIDStrange behavior occurs if you use the device node names (such as /dev/sdc) instead of the device’sUUID. The UUID does not change by reboot or when a path is failed over. Multipathed devicesshow up automatically by their UUID in the /dev/disk/by-id directory.The default settings in mdadm.conf and lvm.conf files do not work properly with multipatheddevices. By default, both md and LVM2 scan only the physical devices, and they ignore anysymbolic links to devices and Device Mapper multipath I/O (DM-MPIO) devices. When managingDM-MPIO devices, you want the opposite behavior, so they ignore all physical devices, and scanonly the devices listed in the /dev/disk/by-id directory.To avoid problems, do the following:1 In a terminal console, log in as the root user.2 Open the /etc/mdadm.conf file in a text editor, then modify the Devices variable to scanfor devices in the /dev/disk/by-id directory, as follows:DEVICE /dev/disk/by-id/*After you start multipath I/O services, the paths are listed under /dev/disk/by-id as thesenames are persistent. They are identical to their non-multipathed names.