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Hitachi Lightning 9900™ User and Reference Guide 25
2.4 Intermix Configurations
2.4.1 RAID-1 & RAID-5 Intermix
RAID technology provides full fault-tolerance capability for the disk drives of the 9900
subsystem. The 9900 supports RAID-1, RAID-5, and intermixed RAID-1 and RAID-5
configurations, including intermixed array groups within an array domain. The cache
management algorithms (see section 3.3.1) enable the 9900 to stage up to one full RAID
stripe of data into cache ahead of the current access to allow subsequent access to be
satisfied from cache at host channel transfer speeds.
2.4.2 Hard Disk Drive Intermix
Figure 2.7 illustrates an intermix of hard disk drive types. All hard disk drives in one array
group must be of the same capacity and type. The 18-GB, 47-GB, 73-GB, and 146-GB HDDs
can be attached to the same ACP pair. The 180-GB HDDs should not be intermixed with other
HDD types behind the same ACP pair. See the notes under Table 2.3 for important
information on 9900 subsystems which contain 180-GB HDDs.
4th
ACP
Pair
2nd
ACP
Pair
3rd
ACP
Pair
1st
ACP
Pair
RAID group
RAID5: 3D+1P
RAID1: 2D+2D
RAID group of 180-GB HDD
RAID group of 180-GB HDD
RAID group of 47-GB HDD
RAID group of 18-GB HDD
9900
Controller
Disk Arra
y
Unit
Disk Arra
y
Unit
Disk Arra
y
Unit
Disk Arra
y
Unit
Disk Arra
y
Unit
Disk Array
Unit
Figure 2.7 Sample Hard Disk Drive Intermix