Configuring and Using Mirrored Volumes and RAID-5 Volumes

This section discusses using features that are available in Windows 2000 Server software to implement mirrored volumes and RAID-5 volumes. It does not discuss configuring or using hardware RAID arrays.

Creating a Mirrored Volume or RAID-5 Volume

If you are using all SCSI disks, it is a good idea to use the same translation on all SCSI controllers on disks in a mirrored volume or RAID-5 volume. Disable translation when you do not need to multiple-boot with MS–DOS or have a system volume or boot volume larger than 1 gigabyte (GB).

When you create a mirrored or RAID-5 volume, Disk Management allocates unused space from each dynamic disk that you select.

For information about creating mirrored and RAID-5 volumes, see Windows 2000 Server Help.

Creating a Mirrored Volume

If you need to multiple-boot with MS–DOS, Windows 95, or Windows 98, you cannot mirror your system volume. If you need a boot volume larger than 1 GB, you need to enable translation.

When you want to create a mirrored volume, the original volume that you want to mirror must already exist. You must have an area of unused space on a dynamic disk at least as large as the original volume on another disk connected to the computer.

If the unused space that you select for the volume on the shadow disk is larger than the existing volume, the remaining space is unused and can be used to create other volumes.

Creating a RAID-5 Volume

To create a RAID-5 volume, you must have at least three unused areas on different dynamic disks connected to the computer. As with a mirrored volume, if the areas of unused space that you select for a RAID-5 volume are not all the same size, the space left over can also be used for other volumes.

When using a RAID-5 volume, performance is better if you put the operating system and page file on the volume and disks used for the RAID-5 volume. You can use different types of controllers for the operating system and the RAID-5 volume when you have them on separate controllers. For more suggestions, see "RAID-5 Volumes" earlier in this chapter.

Configuring the System Partition on a Mirrored Volume

If your system volume is on a SCSI disk, you need to have the BIOS enabled on the SCSI controller, or the system cannot find the MBR. If you have created a mirror of your system volume by using two SCSI controllers, make sure that you are using the same translation on both controllers.



Note that you cannot create a dynamic volume within Setup. If you must delete a dynamic volume from within Setup, delete all volumes on the disk. This reverts the drive to a basic drive and results in the loss of all data on that drive.

Use the translation feature on SCSI controllers to set the translation mode. Because you need to disable the BIOS on the second controller, Windows 2000 always translates the geometry of the shadow volume to 32 sectors per track and 64 heads per cylinder. Therefore, it is important to make sure that the SCSI controller for the original disk is using the same translation. When the BIOS is enabled, most SCSI controllers default to a large disk translation scheme if the disk is larger than 1 GB. The geometry for this translation is 255 heads and 63 sectors. Most SCSI controllers have a method to manually configure the controller to use the 32-sector, 64-head translation. Using 32 sectors and 64 heads on the controller for the original disk ensures that both disks are as close to a true sector-by-sector mirror image as possible. Recovery from failures of the original disk or its controller is much easier if the geometry of both disks is the same. The only disadvantage is that older controllers that do not support Interrupt 13 Extensions need the system volume to be within the first 1 GB, or 1024 cylinders, of the disk. Windows 2000 takes advantage of Interrupt 13 Extensions, which makes it possible for the system volume to reside on large volumes that exceed the 1024 cylinder limit

Disabling the controller BIOS is different from turning off translation. Problems occur because you need to have the BIOS enabled on the first controller to start the computer from the hard disk. If you do not turn off translation on both controllers, and the first controller fails, you need to enable the BIOS on the second controller. The translation on the second disk is now different than when you low-level formatted it, and you cannot use the disk.



If you disable the BIOS on both controllers, translation is automatically disabled as well. However, you cannot start up from the hard disk if the BIOS is disabled.

If you receive the message "Drive is too small" when you try to reconstruct the mirrored volume after the failure of the original disk, it is likely that the translation is not consistent.

Having two different SCSI controllers complicates restarting the computer in the event of a hardware failure. If you use two different SCSI controllers in your mirrored volume, you need to have a different SCSI device driver for each controller.



The term duplexed mirrored volume means that each disk in the mirrored volume has its own disk controller.

You can use Enhanced Integrated Drive Electronics (EIDE) controllers for a mirrored volume of the system volume. EIDE disks usually require motherboard BIOS support for logical block addressing (LBA), and each motherboard usually performs LBA in the same way for all EIDE disks.



If you are going to mirror an EIDE disk with a SCSI disk, do not mirror the system volume. However, you can mirror your boot volume.

When the shadow disk or controller fails, recovery is the same as recovering from any mirrored volume failure. Follow the guidelines for identical disks and controllers described earlier in this chapter. For more information about rebuilding the mirrored volume when you have replacement hardware, see "Repair, Recovery, and Restore" in this book and Windows 2000 Server Help.

When the original disk or controller fails, Windows 2000 seamlessly starts using the shadow disk for all accesses. For this reason, a problem can go undetected until you try to restart the computer. In this case, you might need to remove power from the failed disk or remove it from the SCSI bus before attempting to start from the shadow volume using the Windows 2000 startup floppy disk.



If you use a computer with an Extended Industry Standard Architecture (EISA) volume as the first volume on the primary system disk, you might find that the Windows 2000 startup floppy disk does not start the shadow drive. This is because the Boot.ini is pointing to volume(2) which is not the system volume on the shadow drive. On the shadow drive there is no EISA volume configured as the first volume on the shadow disk. Therefore, you need to change the volume parameter in the Boot.ini to volume(1) as well as changing the disk parameter to point to the shadow drive.



Try both startup paths before a failure, if possible. Also, you should always check Boot.ini if you are using mirrored volumes.