How to install a
Disk Mirror/
Disk Duplex System
for a Novell server?

Alex Yu, Ph.D., CNE

A disk duplex system is like a disk mirror system except that there are two separate controllers for two different hard drives.

SCSI Driver

SCSI hard drives should be used for disk mirroring. Some new users of SCSI devices may be panic when they see the message "no BIOS is installed" at the start up. Once I even called the tech support to report this "error message." How embarrassing! Actually the SCSI driver takes over the BIOS to prepare the hard drives, and that's why the "error message" is normal.

Equal DOS partition size

The manual said that disk duplex can be done even if the size of the two hard drives are not the same. The consequence is that you would waste some disk space when the smaller drive mirrors the large one. It is correct in the Netware partition, but not in DOS partition. When you create the DOS partitions in the hard drives, the size of the two DOS partitions must be exactly equal.

Disable BIOS translation for DOS > 1G

If the hard drive size of your server is more than 1G, you must turn off the BIOS translation for DOS > 1G in both SCSI host adapters. It is counter-intuitive because you may think it must be on to let the large hard drives being detected. However, Netware has its own partition format that is completely different from DOS'. Usually you press Control-A to access SCSI adapters. After this function in both SCSI adapters has been disabled, you can follow the Netware manual to duplex your hard drives.

Load the disk driver twice

Although the Netware installer is packed with many disk drivers, you had better use the disk driver from the hardware manufacturer. Keep in mind that you have to load the disk driver twice. Netware is intelligence enough to calculate the slot number for each driver. Simply accept whatever Netware assigns to the system. Tragedies begin when you think that you are smarter than Novell.

Check the hard drive size

During the installation a prompt would tell you that the hard drive size may look smaller than you expect. It would be fine if it is about 20 meg smaller. However, if you lost 200-300 meg, it is likely that the partition is wrong. Go back to the beginning and re-install the server! Patience is virtue!

Copy files of DOS partition to the second drive

It is important to note that Netware only mirrors the Netware partition, but not the DOS partition. After the installation, you have to copy the files including C:\NWSERVER to the D: drive in order to make D: bootable.

Alter the boot sequence to simulate a failed drive

To test whether your server is really duplexed, you may alter the boot sequence. In other words, you want to know whether the server can be loaded from a second set of controller, cable, and hard drive when the primary one fails. Usually the server boots from the hard drive attached to the on board controller. When the computer is starting up, go to BIOS (the key to access BIOS varies; it may be F1, F2, or DEL). In the BIOS, change the startup from embedded device to on slot device. If the on slot device is chosen, then pick the other one. Afterwards, exit BIOS and reboot the machine. If the server can be loaded successfully, you have a disk duplex system! If not, check whether the DOS partition is set to Active by using FDISK.

Blind spot in troubleshooting a failed mirrored disk

As mentioned before, a disk duplex system is that two controllers attach to two hard drives. However, do not focus on only the controllers and the hard drives when the system fails. To put it correctly, a disk duplex system is that two controllers use two SCSI cables to connect with two hard disks. Controllers and hard drives are quite reliable. It is more likely that SCSI cables fail. Once I spent several hours to troubleshoot an unrecognized hard disk but indeed the problem was the SCSI cable.

Remirror your drive after failure

You hope that your server can run forever, right? Well, either the controller, cable, or hard drive may break down someday. What is the point to have a disk duplex system? The server should continue to provide service with the second hard drive. However, after you replace the bad hard drive with a new one, the two hard drives no longer synchronize. To re-synchronize them, you have to access the disk mirror option by typing load install in the console. The system will automatically copy the data from the existing hard drive to the blank new one.

Delete the data in the bad volume

However, it would be tricky if you have a malfunctioning SCSI cable or controller rather than a bad hard drive. After you have replaced the bad cable or controller, the original hard drive comes back online and the system would ask you to salvage the data and then give it a name. If you attempt to re-synchronize the two drives, the system would tell you that both hard drives carry data and it does not know which one should be copied over which one. So Netware would ask you to delete the data of one of the drives in order to re-mirror them. Therefore, when you salvage the drive that was off-line, you should rename the volume to something obvious such as "junk" or "rubbish." Make sure you delete "junk" and let "sys" to be copied over "junk."

Good luck!



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