Sun Fire V445 Server Administration Guide - SCN Research

On the Sun Fire V445 server, you can configure hardware disk mirroring using the
SAS controller. This provides higher performance than with conventional software
mirroring using volume management software. For more information, see:
■ “Creating a Hardware Disk Mirror” on page 118
■ “Deleting a Hardware Disk Mirror” on page 120
■ “Performing a Mirrored Disk Hot-Plug Operation” on page 121
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 disk 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.
About Hardware Disk Mirroring
On the Sun Fire V445 server, the SAS 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,
only one device (the master) appears in the device tree. The mirrored device (the
slave) is invisible to the OS, and is accessed only by the SAS controller.
116 Sun Fire V445 Server Administration Guide • August 2006