RAID and Subsystem Architectures Assigning Hosts to Storage
Drive Assignment: Host Level
Logical Disks
Host A
Drive D (2 GB)
Drive E (500 MB) Drive F (500 MB)
SCSI LUNs 5 x 1GB
SCSI ID 3 SCSI ID 4
SCSI ID 1
SAN
Host B
Drive D (1GB)
Drive E (1GB)
SCSI ID 2
SCSI ID 0
JBOD
Volume Manager HBA Utility
1GB 1GB 1GB 1GB 1GB
Physical Disks 5 x 1GB
LUN Mapping
When we use a JBOD the Host Bus Adapter, HBA, has the ability to discover all the available disks. We will look at SAN Fabric options for restricting visibility in a later module.
If the host volume manager sees all disks, then we have a possible situation where data could be written to the same disks without any knowledge of any other data that has been written to that disk. This is most likely to cause data corruption by overwriting data that has already been written to that disk.
The HBA configuration utility supports LUN Mapping. This allows us to configure which discovered disks are usable by the host volume manager and creates a map of which disks are advertised through, Mapped, to the volume manager and which disks are blocked from being advertised through.