┌───────────────────┐
││
│ ┌───────────┤
│ │ Disk ├───────────────┬────┬───────────┐
│ │ Controller│ │ │ Disk 1 │
│ └───────────┤ │ └───────────┘
│││
│ │ └────┬───────────┐
│ │ │ Disk 2 │
│ │ └───────────┘
││
││
││
└───────────────────┘
Figure 12. RAID-1 (Disk Mirroring)
Disk mirroring involves duplicating the data from one disk onto a second disk
using a single controller.
Disk duplexing is the same as mirroring in all respects, except that the disks are
attached to separate controllers. The server can now tolerate the loss of one
disk controller, as well as or instead of a disk, without loss of the disk
subsystem′s availability or the customer′s data. Since each disk is attached to a
separate controller, performance and throughput may be further improved.
┌───────────────────┐
││
│ ┌───────────┤
│ │ Disk ├────────────────────┬───────────┐
│ │ Controller│ │ Disk 1 │
│ └───────────┤ └───────────┘
││
│ ┌───────────┤
│ │ Disk ├────────────────────┬───────────┐
│ │ Controller│ │ Disk 2 │
│ └───────────┤ └───────────┘
││
││
└───────────────────┘
Figure 13. RAID-1 (Disk Duplexing)
1.6.6.3 RAID-1 Enhanced - Data Strip Mirroring
RAID level 1 supported by the IBM PC Server array models provides an
enhanced feature for disk mirroring that stripes data and copies of the data
across all the drives of the array. The first stripe is the data stripe; the second
stripe is the mirror (copy) of the first data stripe, but, it is shifted over one drive.
Because the data is mirrored, the capacity of the logical drive, when assigned to
RAID 1 Enhanced, is 50 percent of the physical capacity of the hard disk drives in
the array.
Chapter 1. IBM PC Server Technologies 25