Specifications

26 en | RAID Planning SCSI to SATA RAID Subsystem | Administrator’s Manual
F.01U.027.802 | V1 | 2006.11 Bosch Security Systems
2.3 Operation Theory
2.3.1 I/O Channel, Host ID, and LUN
Depending on the interface used by a RAID system, a SCSI channel (channel bus) can connect
up to 15 drives (excluding the RAID controller itself). A Fibre Channel supports up to 126
drives in a loop. Depending on the subsystem design, a SCSI-based subsystem may have eight
(8) disk drives connected through a drive channel while a SATA-based subsystem has one
channel dedicated to each of its disk drive. Each device occupies one unique ID.
The illustration belows shows the idea of mapping a system drive to host ID/LUN combina-
tions (see Figure 2.3). The host ID is like a cabinet, and the drawers are the LUNs (LUN is
short for Logical Unit Number). Each cabinet (host ID) contains up to 32 drawers (LUNs). Data
can be made available through one of the LUNs of a host ID. Most host adapters treat a LUN
like another device.
Fig. 2.3 SCSI ID/LUNs
2.3.2 Grouping Drives into an Array
Fig. 2.4 Connecting Drives
The logical view of the connection between RAID controller(s) and disk drives should be simi-
lar to the one shown above. Drives are connected through I/O paths on a back-end PCB that
have been designated as drive channels.
The next diagram shows two logical configurations of drives and the physical locations of its
members. There is no limitation on the locations of spare drives or drive members.