67Chapter C - Quick-Setupyou to continue your work without having to wait. The firmware will always ensure that bothdrives contain identical data. If a drive should fail during your working session, the fir m-ware is able to continue to work without interruption because it uses the second drive.RAID 1 is a rather expensive method of redundancy because it requires the double numberof drives. It is a distinctive characteristic of the firmware that all cache drives receive theirown number, the so-called cache drive number. This number does not depend on thephysical location of the disks forming the cache drive on a SCSI channel.Level 3:On the highest level of hierarchy, the firmware forms the host drives. In the end, only thesehost drives can be accessed by the host operating system of the computer. Drives C, D, etc.under MS-DOS, OS/2, etc. are always referred to as host drives by the firmware. The sameapplies to NetWare- and UNIX-drives. The firmware automatically transforms each newlyinstalled cache drive into a host drive. This host drive is then assigned a host drive numberwhich is identical to its cache drive number. Disk arrays of redundancy levels RAID 4, 5 and10 (with RAIDYNE) are installed on this level, using the cache drives of level 2 as comp o-nents. The firmware is capable of running several host drives of the most various kinds atthe same time. An example for MS-DOS: drive C is a RAID 5 type host drive (consisting of 5SCSI hard disks), drive D is a single hard disk, and drive E is a CD-ROM com municatingwith RAIDYNE through corelSCSI and the GDT ASPI manager.In GDTSETUP, each level of hierarchy has its own special menu:level 1 ÷ menu: Initialize Diskslevel 2 ÷ menu: Set up Cache Driveslevel 3 ÷ menu: Configure Host DrivesGenerally, each installation procedure passes through these three menus, starting withlevel 1. Therefore:4 First initialize the physical drives.4 Then install the cache drives (and, if desired, their correspondingmirror drives).4 Then the host drives (e.g. disk arrays with RAID 0, 4 and 5) are cre-ated on the host drive level.C.5 Using CD-ROMs, DATs, Tapes, etc.A SCSI-device that is not a SCSI hard disk or a removable hard disk, or that does not b e-have like one, is called a Not Direct Access Device.Such a device is not configured with GDTSETUP and does not form cache or hostdrives. SCSI-devices of this kind are either run through the ASPI interface (Advanced SCSIprogramming Interface) (MS-DOS, Windows, Novell NetWare or OS/2), or are directly a c-cessed from the operating system (UNIX, Windows NT). For more information on how touse these devices, please refer to the according chapters of this manual.Note: hard disks and removable hard disks are called Direct Access Devices. However, there aresome Not Direct Access Devices, for instance certain MO drives, which allow to be operated justlike removable hard disks if they have been appropriately configured before (for example bychanging their jumper setting).But now enough about the dry theory.
