HP Compaq Integrated Smart Array Controller - Manual (Page 126)

B-20 Compaq Integrated Smart Array Controller User Guide
Compaq Confidential – Need to Know Required
Writer: CDresden Project: Compaq Integrated Smart Array Controller User Guide Comments:
Part Number: 153236-001 File Name: i-appb Understanding Drive Arrays.doc Last Saved On: 8/27/99 11:35 AM
Software-Based Drive Mirroring
IMPORTANT: Compaq strongly recommends using hardware-based fault tolerance
instead of software-based fault tolerance. Hardware-based fault tolerance provides a
much more robust and controlled environment for fault-tolerance protection.
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 and you will not be able to retrieve your data.
Software-based drive mirroring is a function of the operating system. Refer to
the documentation included with your operating system for instructions on
implementing this feature.
For more information on hardware versus software fault tolerance, consult the
white paper section of the Compaq Storage website:
http://www.compaq.com/support/techpubs/whitepapers/
Recovering from Drive Failure
The purpose of fault-tolerant configurations on the Integrated Smart Array
Controller is to protect against data loss due to drive failure. Although the
Integrated Smart Array Controller firmware is designed to protect against
normal drive failure, it is imperative that the system operator perform the
correct actions to recover from a drive failure without inadvertently inducing
any additional drive failures.
Multiple drive failures in the same array generally result in data loss;
exceptions include failures following activation of a spare drive, and failure of
drives in a mirroring configuration that are not mirrored to one another.