Windows NT Disk Administrator


Disk Administrator is the main tool in Windows NT for maintaining and configuring hard disks. With Disk Administrator, you can create and remove partitions and logical drives and format disks. It lets you set up volume sets and implement some performance and fault tolerance features such as disk mirroring, striping, and striping with parity.

When you start Disk Administrator for the first time (its icon is in the Administrative Tools program group in NT 3.51, and under the Administrative Tools folder in NT 4.0), it will ask you for permission to write a signature on the disk. The signature helps Disk Administrator identify the disk, even if you shift the disk to a different controller. Disk Administrator will not let you proceed unless you grant signature permission and will repeat this request when you add new disks to the system.

Disk Administrator displays odd behavior in NT 3.51. Often, when you start Disk Administrator, it disappears behind other open windows. You have to cycle through the open windows or minimize them to get to it.

When you first open Disk Administrator, you will see something like Screen 1. In NT 4.0, Disk Administrator has more capabilities and more customization options than in NT 3.51. For example, CD-ROM drives appear just like any other disk on a display. In the future, I expect a variety of devices to show up here, including Digital Video Disc (DVD), optical, Jaz drives, and so on. You can adjust the Region Display to show each region of the drives as an equal area or proportionally spaced. But the easiest way is to let Disk Administrator decide how to show the regions. Color coding will show volume sets and stripe sets.

Allocating Space
Use Disk Administrator to allocate the space remaining on your hard drives after you install your system's partition. Suppose you install NT on a new computer and, during installation, allocate space only for the C partition. Disk Administrator can allocate the remaining space on the same disk or the space on the other disks. Simply select (with the mouse) an area of free space, and select Partition, Create to add a partition. Disk Administrator does not add the partition at this point, but it shows up on the screen. This approach ensures that you can still back out of changes if you make a mistake and explains why you cannot format the disk yet--Tools, Format is dimmed. You must exit the utility or select Partition, Commit Changes Now to implement changes you make in Disk Administrator. Once you create the new partition, you can format the assigned space.

Be careful how you allocate this space. If you make all the free space an extended partition and then assign logical drives in the extended partition, you can remove the partition later, even with FDISK, a DOS-based hard disk partition-management utility. But if you create NT File System (NTFS) drives as individual non-DOS drives, the only way to remove them is either with Disk Administrator or using the NT Setup program. If you remove NT and then try to use FDISK from DOS to remove these partitions, FDISK will not remove the partitions, because they contain logical drives. FDISK cannot identify the logical drives to remove them. Sometimes FDISK will remove the partitions if you ignore the warning messages, but often it will not. You can work around this situation with a program such as PartitionMagic, a hard disk management utility from PowerQuest. (For a description of this utility, see "PartitionMagic.")

Because Microsoft encounters this problem in classrooms, an unsupported utility, delpart.exe, comes with Microsoft's NT class instructor materials. You can download the compressed utility as drlprt.exe, with instructions, from Microsoft's bulletin boards (BBS number 206-936-6735), Web site ( com), or CompuServe forum (GO MICROSOFT). Be aware that delpart.exe will remove any partition, so use it carefully. If you have SCSI drives, a low-level format will remove any existing partitions, but reformatting is a last resort.

The Windows NT 4.0 version of Disk Administrator adds the capability to set the cluster or allocation unit size for NTFS disks. (The FORMAT /A option in NT 3.51 lets you set these sizes from the command prompt, but this capability is not available in Disk Administrator.) NT 4.0 Disk Administrator uses a default cluster size of 4096 bytes. Valid cluster sizes are 512, 1024, 2048, and 4096 bytes when set from Disk Administrator and up to 64KB from the command line. The size of the logical drive determines cluster sizes on File Allocation Table (FAT) disks, of course.

Assigning Drive Letters
NT is more flexible than DOS for assigning drive letters. For example, NT does not require you to assign the letters for the hard disk drive first, and then for the CD-ROM drives. This flexibility lets you avoid having to reassign drive letters. (Some software keeps track of the drive from which you install it, and updates can be awkward if the drive letter has changed.) Your CD-ROM can still be drive E, with a hard disk designated as drive F. If this notation offends your sense of tradition, you can assign the CD-ROM a letter such as M or N, which will leave plenty of room for adding disk drives later, and assign the next available letter to the new drives.

To assign a drive letter in NT 3.51, choose Tools, Assign Drive Letter, or Assign CD-ROM Drive Letter. In NT 4.0, right-click the drive to summon the Properties shortcut menu. From Properties, as you see in Screen 2, you can assign a new drive letter. With either version of NT, pick the drive letter, and Disk Administrator assigns it immediately. If you get a message that the drive letter cannot be reassigned because a lock is on the drive, you may have an open application that is using a file on this drive. Or perhaps File Manager or Explorer is open, pointing to this drive, and maybe even someone is connected to this drive across the network. You can close the application, you can drop network connections through the Server icon in Control Panel, or you can reboot.

NT 4.0 Drive Sharing
New to NT 4.0 is the ability to share a drive on the network from within Disk Administrator. Right-click the drive to invoke the shortcut menu. From here, use the Share tab on this menu to share the drive, and assign permissions on the share from the Security tab on the shortcut menu. As always in NT, the default share permission gives Full Control to Everyone. To improve your security, change this configuration to give permission only to users who need access to the share.

NT Server offers several features in addition to those in NT Workstation. These features provide the fault tolerance necessary in critical server situations. For example, disk mirroring duplicates the data written to one disk to a second disk. If a primary disk fails, the mirror disk takes over with no data loss. You can even mirror the operating system files, which is an excellent idea for mission-critical servers.

Disk mirroring is as easy to set up as any other option in Disk Administrator. Just select the drive to mirror and, on a different physical disk, an area of free space that is at least as large. Fault Tolerance, Establish Mirror appears in Disk Administrator only if you are running NT Server. Establish Mirror creates the mirror set, using exactly as much space on the mirror drive as you assigned to the primary drive. Suppose you use two controllers (disk duplexing). For additional redundancy, you simply use Disk Administrator to mirror two drives, one on each controller.

The disadvantage of mirroring or duplexing is that half your total disk space in the mirror set is no longer available for data. But mirroring the system partition can be worthwhile, for safety. And as an added benefit, mirroring will increase speed on data reads by reading from both disks or reading different files from each of the two disks simultaneously. This concept is a good idea, but the NT mirroring software does not implement it. You can implement fault tolerance at the hardware level, with additional functionality, as Joel Sloss describes in "RAID Performance and NT," page 56. The following discussion covers software-level fault tolerance.

Volume Sets
NT does an impressive job of isolating the applications from the hardware. And one of the best ways NT uses is a volume set. A volume is an area of disk that you have assigned as a logical drive. NT's volume set feature lets you combine one or more disks or free space on multiple disks into what appears to be one logical disk drive. The logical drive appears in File Manager as one drive with a total size of all the combined areas. Through the I/O Manager, applications write to the logical drive and have no way of telling that the drive is actually several physical drives.

Building a volume set is easy. Just select the areas you want to combine, and choose Partition, Create Volume Set. You can format the volume set as either FAT or NTFS.

A volume set has two slight disadvantages: If one drive fails, you cannot recover the remaining data. Combining multiple drives increases the number of points of potential failure. And you cannot remove pieces of a volume set, so once you build one, the only way to reassign the disk regions is to delete the entire volume set.

On the positive side, you can extend a volume set without losing the data it contains. Suppose you have a database on a 500MB drive. The database is almost at full capacity, and you need to extend the space allocated to it. You can extend a volume set if it is formatted as NTFS. Select the existing volume (which can be a single region of the disk, not a volume set) and select an area of free space on the same drive or another drive. Partitions, Extend Volume Set lets you add the new space to the existing volume to give your database some breathing room.

You will have to stop and restart NT to add the new space, but that inconvenience is minor compared to running out of disk space. If you format your disk as FAT, you cannot extend the volume. However, you can convert it to NTFS and then extend it, without losing data.

Striping and Striping with Parity
Disk striping writes data in 64K pieces to multiple disks to create a stripe set. The process distributes a file evenly across all the disks in the set, so each disk, or region of a disk, in the set must be the same size.

You see the benefit of disk striping in read operations, when multiple disk drive heads can read the data segments simultaneously and reassemble those segments in memory. However, if any disk fails, you cannot recover the file. So use striping only for applications such as read-only databases or for storing large image files, where you have a good backup handy if you need it.

People sometimes refer to striping as RAID (Redundant Arrays of Inexpensive Disks) Level 0, which is a suitable designation because it provides zero redundancy. Striping is available in NT Workstation.

To set up a stripe set, select two or more areas on different physical disks. Choose Partition, Create Stripe Set to build the stripe set. You cannot build a stripe set using two different areas on the same physical disk--this idea makes no sense. Screen 3 shows a stripe set.

NT Server adds striping with parity. This combination offers the fast read capability of striping and adds built-in redundancy. Parity information is computed and written with the data. To build a stripe set with parity, you must have three or more disks. Select the areas from the disks, and click Fault Tolerance, Create Stripe Set with Parity in Disk Administrator to build the stripe set. As with striping, this routine spreads the data equally among the disks, using equal-sized areas on each disk. You can select areas of different sizes, but Disk Administrator will allocate to the stripe set only the space from each drive equal to the smallest area selected. So if you select one area of 500MB and two areas of 600MB, Disk Administrator will use only 500MB from each disk to build the stripe set.

Although Disk Administrator spreads the parity information across the disks, as with the data, the net result is space equivalent to one disk in the set allocated to parity. So in this example, you end up with a stripe set of 1000MB. For parity, you have an additional 500MB that does not show up in File Manager or other utilities. The more disks the better, up to the system limit of 32, of course. With two disks, 50% of capacity goes to parity. With three disks, 33% of capacity goes to parity information. With 10 disks, you lose only 10% of the total space. One caveat: You cannot make the partition that contains your boot and system files part of a stripe set.

If any disk in the set goes down, you can rebuild the data from the remaining disks, using the parity information. The users connected to the server will still be able to read their files, but response time will be slower during data reconstruction. You can replace the disk, and select Fault Tolerance, Regenerate to rebuild the stripe set to the state it was in before the disk failure.

Keep in mind that establishing a stripe set, or a mirror set, and regenerating data can take some time, especially when the disks involved are very large. And although most changes take effect immediately, in some cases, you will have to start and stop NT before the changes become effective. In these cases, Disk Administrator will inform you and not let you close out of Disk Administrator until you click OK to reboot.

Combining Fault Tolerance Features
You can use any combination of the fault tolerance features. For example, you can combine them to mirror the system partition and then add a volume or stripe set, or both.

Saving the Changes
Disk Administrator changes are stored in the Windows NT Registry, so always back up the Registry and re-create your Emergency Repair Disk when you make changes in Disk Administrator. In fact, Disk Administrator will prompt you to do so. If you do not, and you have to rebuild your system, retrieving the data on volume and stripe sets will be difficult.

NT 3.51 and 4.0 Differences
Disk Administrator in NT 4.0 introduced the shortcut menu, which you invoke by clicking the secondary (usually the right) mouse button. From here, you can set security and auditing on NTFS drives, and you can run utilities such as backup and defragmentation programs. NT 4.0 also lets you customize the user interface more than NT 3.51: You can customize the toolbar and change the colors assigned to stripe sets, volume sets, and so on to suit your preferences, as you can see in the toolbar pulldown in Screen 4. In NT 3.51, the key at the bottom of the screen shows the colors assigned to stripe, volume, and mirror sets even if you do not use these features. NT 4.0 shows only the colors on the key if you have them.

Earlier versions of NT made no distinction between a stripe set and a stripe set with parity on the Disk Administrator display, but NT 4.0 does. And 4.0 adds the table of the disk drives, as shown in Screen 5, to supplement the graphical display with some information about the status of the disks.

Disk Administrator in Windows NT 4.0 implies that you can change the format of a disk from FAT to NTFS or vice versa within Disk Administrator. You can, but you reformat the drive in the process, destroying all the data. You must instead use the convert.exe utility to convert a FAT drive to NTFS with the data intact.

Hot Tip Here's a Disk Administrator suggestion that is not in the manuals: Suppose you have NT installed on a 500MB disk. You want to replace the disk with a new 2GB disk. A tape backup and restore is difficult because you need to run the restore under NT. You could install the new disk alongside the old one and copy all the files over. But when you remove the old disk, NT will not boot from the new disk; the system files do not transfer correctly.

One solution is to build a mirror set: You can create a 500MB partition on the new drive to mirror what you have on the original disk. When you have mirrored all the files, break the mirror set and remove the old hard disk.

For the Future
My wish list for Disk Administrator includes the ability to convert FAT drives to NTFS without having to run a program from the command line. True, this is a feature you don't use very often, but including it in the menu choices wouldn't be that difficult. Aside from that minor complaint, Disk Administrator is an easy-to-use and powerful utility.

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