This is quick how to setup your mirroring with two exactly the same hard disks. It assumes you're building a new system from scratch, and setup mirroring at install time. But let's get something straight first: Software mirroring does not mirror the disks - it mirrors partitions. Thanks to Ed Wilts from Redhat General Newsgroups for this remark. So in this guide I'll show you how to setup your partitions on one disk and mirror them to another. After that, we will learn how to rebuild our mirrored partitions after one disk dies.

Need of Software Mirroring

Mirroring is an easy way of protecting the data, from being lost from disk crash. For example, If you keep your private stuff on one partition you can mirror this partition to another on the second drive, and if one disk fails, you will not lose your data, since you have the exact same copy of your files on the second disk. The same goes for the whole filesystem. If you setup mirroring correct, you might never have to reinstall your system again.

Software Mirroring vs. Hardware Mirroring

• Disk mirroring can be implemented entirely in software. Software mirroring can be less expensive, but it is also slower. Software mirroring requires the host computer to write the mirrored data twice.

• Disk mirroring can be implemented in hardware on the host I/O controller. The burden of writing each bit of data twice is placed upon the I/O controller, which is specifically designed for it.

• Disk mirroring can also be implemented in hardware on an external storage device, such as a RAID array. In this case, mirroring is completely removed from the hosts responsibility

Benefits of Software Mirroring

• Data is backed up as changes are made keeping the backup copy current.

• Immediate access of an up-to-date remote data backup in case of local server failure.

• Rapid disk to disk data recovery from the central server to remote server.

• When data is restored, data loss is reduced to a minimum.

• Continuous real-time disk to disk backup operation minimizes impact on network performance.

• Backup windows all but eliminated.

• Provides 24X7 data availability and disaster recovery.