56 Netra 440 Server System Administration Guide • August 2004
On the Netra 440 server, you can configure hardware disk mirroring using the on-
board Ultra-4 SCSI controller. This provides higher performance than with
conventional software mirroring using volume management software. For more
information, see:
■“To Create a Hardware Disk Mirror” on page 57
■“To Delete a Hardware Disk Mirror” on page 59
■“To Perform a Mirrored Disk Hot-Plug Operation” on page 61
RAID 1 offers the highest level of data protection, but storage costs are high, and
write performance compared to RAID 0 or RAID 5 is reduced since all data must be
stored twice.

RAID 5: Disk Striping With Parity

RAID 5 is an implementation of disk striping in which parity information is
included with each disk write. The advantage of this technique is that if any one
disk in a RAID 5 array fails, all the information about the failed drive can be
reconstructed from the data and parity on the remaining disks.
System performance using RAID 5 will fall between that of RAID 0 and RAID 1;
however, RAID 5 provides limited data redundancy. If more than one disk fails, all
data is lost.

Hot-Spares

In a hot-spares arrangement, one or more hard drives are installed in the system but
are unused during normal operation. This configuration is also referred to as hot
relocation. Should one of the active drives fail, the data on the failed disk is
automatically reconstructed and generated on a hot-spare disk, enabling the entire
data set to maintain its availability.
Hardware Disk Mirroring
On the Netra 440 server, the Ultra-4 SCSI controller supports internal hardware disk
mirroring using the Solaris OS raidctl utility.
A hardware disk mirror created under the raidctl utility behaves slightly
differently than one created using volume management software. Under a software
mirror, each device has its own entry in the virtual device tree, and read/write
operations are performed to both virtual devices. Under hardware disk mirroring,