Windows NT Disk Administrator

ORGANIZING YOUR HARD DISKS WAS NEVER SO SIMPLE

Disk Administrator is the main tool in Windows NT for maintainingand configuring hard disks. With Disk Administrator, you can create and removepartitions and logical drives and format disks. It lets you set up volume setsand implement some performance and fault tolerance features such as diskmirroring, striping, and striping with parity.

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

Disk Administrator displays odd behavior in NT 3.51. Often, when you startDisk Administrator, it disappears behind other open windows. You have to cyclethrough 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 drivesas an equal area or proportionally spaced. But the easiest way is to let DiskAdministrator decide how to show the regions. Color coding will show volume setsand stripe sets.

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

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

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

Formatting
The Windows NT 4.0 version of Disk Administrator adds the capability to setthe cluster or allocation unit size for NTFS disks. (The FORMAT /A option in NT3.51 lets you set these sizes from the command prompt, but this capability isnot available in Disk Administrator.) NT 4.0 Disk Administrator uses a defaultcluster size of 4096 bytes. Valid cluster sizes are 512, 1024, 2048, and 4096bytes when set from Disk Administrator and up to 64KB from the command line. Thesize 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, NTdoes not require you to assign the letters for the hard disk drive first, andthen for the CD-ROM drives. This flexibility lets you avoid having to reassigndrive letters. (Some software keeps track of the drive from which you installit, and updates can be awkward if the drive letter has changed.) Your CD-ROM canstill be drive E, with a hard disk designated as drive F. If this notationoffends your sense of tradition, you can assign the CD-ROM a letter such as M orN, which will leave plenty of room for adding disk drives later, and assign thenext available letter to the new drives.

To assign a drive letter in NT 3.51, choose Tools, Assign DriveLetter, or Assign CD-ROM Drive Letter. In NT 4.0, right-click thedrive to summon the Properties shortcut menu. From Properties, as you see inScreen 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 geta message that the drive letter cannot be reassigned because a lock is on thedrive, you may have an open application that is using a file on this drive. Orperhaps File Manager or Explorer is open, pointing to this drive, and maybe evensomeone is connected to this drive across the network. You can close theapplication, you can drop network connections through the Server icon in ControlPanel, 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 withinDisk Administrator. Right-click the drive to invoke the shortcut menu. Fromhere, use the Share tab on this menu to share the drive, and assign permissionson the share from the Security tab on the shortcut menu. As always in NT, thedefault share permission gives Full Control to Everyone. To improve yoursecurity, change this configuration to give permission only to users who needaccess to the share.

Mirroring
NT Server offers several features in addition to those in NT Workstation.These features provide the fault tolerance necessary in critical serversituations. For example, disk mirroring duplicates the data written to one diskto a second disk. If a primary disk fails, the mirror disk takes over with nodata loss. You can even mirror the operating system files, which is an excellentidea for mission-critical servers.

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

The disadvantage of mirroring or duplexing is that half your total diskspace in the mirror set is no longer available for data. But mirroring thesystem partition can be worthwhile, for safety. And as an added benefit,mirroring will increase speed on data reads by reading from both disks orreading different files from each of the two disks simultaneously. This conceptis a good idea, but the NT mirroring software does not implement it. You canimplement fault tolerance at the hardware level, with additional functionality,as Joel Sloss describes in "RAID Performance and NT," page 56. Thefollowing 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 anarea of disk that you have assigned as a logical drive. NT's volume setfeature lets you combine one or more disks or free space on multiple disks intowhat appears to be one logical disk drive. The logical drive appears in FileManager as one drive with a total size of all the combined areas. Through theI/O Manager, applications write to the logical drive and have no way of tellingthat 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 eitherFAT or NTFS.

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

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

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

Striping and Striping with Parity
Disk striping writes data in 64K pieces to multiple disks to createa stripe set. The process distributes a file evenly across all the disksin 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 diskdrive heads can read the data segments simultaneously and reassemble thosesegments in memory. However, if any disk fails, you cannot recover the file. Souse striping only for applications such as read-only databases or for storinglarge image files, where you have a good backup handy if you need it.

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

To set up a stripe set, select two or more areas on different physicaldisks. Choose Partition, Create Stripe Set to build the stripe set. Youcannot build a stripe set using two different areas on the same physicaldisk--this idea makes no sense. Screen 3 shows a stripe set.

NT Server adds striping with parity. This combination offers the fast readcapability of striping and adds built-in redundancy. Parity information iscomputed and written with the data. To build a stripe set with parity, you musthave three or more disks. Select the areas from the disks, and click FaultTolerance, Create Stripe Set with Parity in Disk Administrator tobuild the stripe set. As with striping, this routine spreads the data equallyamong the disks, using equal-sized areas on each disk. You can select areas ofdifferent sizes, but Disk Administrator will allocate to the stripe set only thespace from each drive equal to the smallest area selected. So if you select onearea of 500MB and two areas of 600MB, Disk Administrator will use only 500MBfrom each disk to build the stripe set.

Although Disk Administrator spreads the parity information across thedisks, as with the data, the net result is space equivalent to one disk in theset allocated to parity. So in this example, you end up with a stripe set of1000MB. For parity, you have an additional 500MB that does not show up in FileManager or other utilities. The more disks the better, up to the system limit of32, 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% ofthe total space. One caveat: You cannot make the partition that contains yourboot and system files part of a stripe set.

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

Keep in mind that establishing a stripe set, or a mirror set, andregenerating data can take some time, especially when the disks involved arevery 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 thesecases, Disk Administrator will inform you and not let you close out of DiskAdministrator 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 orstripe set, or both.

Saving the Changes
Disk Administrator changes are stored in the Windows NT Registry, so alwaysback up the Registry and re-create your Emergency Repair Disk when you makechanges in Disk Administrator. In fact, Disk Administrator will prompt you to doso. If you do not, and you have to rebuild your system, retrieving the data onvolume 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 invokeby clicking the secondary (usually the right) mouse button. From here, you canset security and auditing on NTFS drives, and you can run utilities such asbackup and defragmentation programs. NT 4.0 also lets you customize the userinterface more than NT 3.51: You can customize the toolbar and change the colorsassigned to stripe sets, volume sets, and so on to suit your preferences, as youcan see in the toolbar pulldown in Screen 4. In NT 3.51, the key at thebottom of the screen shows the colors assigned to stripe, volume, and mirrorsets even if you do not use these features. NT 4.0 shows only the colors on thekey if you have them.

Earlier versions of NT made no distinction between a stripe set and astripe set with parity on the Disk Administrator display, but NT 4.0 does. And4.0 adds the table of the disk drives, as shown in Screen 5, tosupplement the graphical display with some information about the status of thedisks.

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

Hot TipHere's a Disk Administrator suggestion that is not in the manuals: Supposeyou have NT installed on a 500MB disk. You want to replace the disk with a new2GB disk. A tape backup and restore is difficult because you need to run therestore under NT. You could install the new disk alongside the old one and copyall the files over. But when you remove the old disk, NT will not boot from thenew disk; the system files do not transfer correctly.

One solution is to build a mirror set: You can create a 500MB partition onthe new drive to mirror what you have on the original disk. When you havemirrored 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 FATdrives to NTFS without having to run a program from the command line. True, thisis a feature you don't use very often, but including it in the menu choiceswouldn't be that difficult. Aside from that minor complaint, Disk Administratoris an easy-to-use and powerful utility.