Mirroring and Duplexing

You can protect your data on disk by mirroring or duplexing disk partitions.

Mirroring stores the same data on separate disks on the same controller channel; duplexing stores the same data on separate disks on separate controller channels. Duplexing can also include using two different drivers. Duplexing is the preferred method since two channels rarely fail simultaneously.

In the following illustration, several smaller disks are mirrored to partitions on one larger disk.

Partitions to be mirrored must have Hot Fix enabled. For information about Hot Fix, see Redirecting Bad Blocks.

When Hot Fix is enabled, a portion of the partition is set aside as the Hot Fix/Mirror object, which holds data tables for both Hot Fix and mirroring. The tables store information about what data blocks are bad, what blocks have been redirected, what partitions are mirrored, and whether the partitions are synchronized or not.

If you do not enable Hot Fix, then no Hot Fix/Mirror object is created and neither mirroring nor Hot Fix redirection can take place. Remember that it is much easier to set up Hot Fix when you create the partition. To add Hot Fix later, you must delete the volumes from the partition, add Hot Fix, then restore the volumes from a backup.

Following are some considerations to keep in mind when mirroring partitions:

Hot Fix must be enabled on all the partitions to be mirrored. You cannot mirror partitions that do not have a Hot Fix Redirection Area.
Mirroring requires the NetWare Hot Fix redirection areas on each partition to be the same size. If they are not the same size, NWCONFIG adjusts the larger one to the size of the smaller one when you set up mirroring.
Although you can mirror one partition to as many as eight other partitions, mirroring two partitions is usually sufficient fault tolerance for most systems.
If a mirrored disk fails and cannot be accessed by the server, you can unmirror the hard disks and salvage the volume from the functional disk. See Recovering Data from an Out of Sync Disk.
If you want to remove a hot-plug mirrored disk without bringing down the server, you must unmirror the disk first. See Unmirroring Partitions.

For information about how to set up mirroring and duplexing, see Mirroring and Duplexing Partitions.