Controller Duplexing; Software-Based Drive Mirroring - Compaq 219700-001 - ProLiant - 1500 Reference Manual

Controller Duplexing

Some operating systems support controller duplexing, a fault tolerance feature
that requires two SMART-2DH Array Controllers. With duplexing, the two
controllers each have their own drives that contain identical data. In the
unlikely event of a SMART-2DH Controller failure, the remaining drives and
SMART-2DH Controller service all requests.
Controller duplexing is not the same as duplexing the SCSI buses on a single
SMART-2DH Controller. Controller duplexing is a function of the operating
system and takes the place of other fault tolerance methods. Refer to the
documentation included with your operating system for implementation.
Compaq recommends using hardware-based fault tolerance instead of
controller duplexing. Hardware-based fault tolerance provides a much more
robust and controlled environment for fault tolerance protection.
If you choose controller duplexing, configure each SMART-2DH Controller
with RAID 0 to achieve maximum storage capacity. In addition, the following
fault-tolerant features will not be available: Online Spare, Auto Reliability
Monitoring, Interim Data Recovery, and Automatic Data Recovery.

Software-Based Drive Mirroring

Some operating systems support software-based drive mirroring as a fault
tolerance feature. Software drive mirroring resembles hardware based drive
mirroring (RAID 1), except that the operating system mirrors logical drives
instead of physical drives.
A pitfall of software-based drive mirroring is that the operating system
believes each logical drive is a separate physical drive. If you mirror logical
drives in the same array and a physical drive fails, both logical drives in the
mirrored pair will fail. You will not be able to retrieve your data.
Because software-based drive mirroring is a function of the operating system,
refer to the documentation included with your operating system for
implementation.
Writer: Pamela King Project: SMART-2DH Array Controller Reference Guide Comments: 295469-002
File Name: K-APPD.DOC Last Saved On: 2/27/98 12:06 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
SMART-2DH Array Controller Reference Guide
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