Difference: FibreAttach (2 vs. 3)

Revision 32009-02-10 - neilb

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Attaching a linux box to a SAN

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  This is fine for static configurations where SCSI disks don't come and go but, in a SAN environment where new volumes and storage arrays are routinely added and removed, this simplistic naming convention creates real problems. If a new volume is created on a storage array, this will often result in many existing volumes being discovered after the new volume, and hence being assigned a different SCSI device name.
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If you have just added a new volume to an array, you will probably need to get the HBA to rescan the bus to detect it. For QLogic cards, the following should work
  echo "scsi-qlascan" > /proc/scsi/qla2xxx/1
  rescan-scsi-bus.sh -c -l -w
Though you will have to use the path appropriate to your HBA and port in use. And obtains the rescan-scsi-bus.sh script from the web.
 Under FC5, the SCSI stack now creates a soft link to each partition it finds on any attached disk (volume), whether it be local or on a SAN, in the /dev/disk/by-id directory. These soft links are based on the unique SCSI identifiers for the associated volumes. In effect, the SCSI stack is now automatically doing the work that the FC3 udev service did, with no configuration required; with the slight difference that the links are now per partition rather than being per disk (volume).

In the following example, there are five volumes, the first three of which have just one partition, the fourth has two partitions and the fifth has currently no partitions :-

 
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