DisksConcepts | Windows Server 2003 in a Nutshell

DisksConcepts

Like previous versions of Microsoft Windows, WS2003 supports older, fixed-disk technologies, but it also supports some new technologies that increase performance and make disk management easier.

Types of Disk Storage

WS2003 supports two types of fixed-disk storage:

Basic storage: This storage technology is the same as that of legacy versions of Microsoft Windows, including NT 4.0 and 3.51, Windows 98, and Windows 95. Basic storage divides disks into a limited number of partitions and logical drives and supports advanced features such as volume sets, stripe sets, stripe sets with parity, and mirror sets.
Dynamic storage: This technology, available in WS2003 and W2K Server, divides disks into an unlimited number of volumes. Dynamic storage supports advanced features such as spanned volumes, striped volumes, RAID-5 volumes, and mirrored volumes .

In addition, WS2003 supports certain types of removable storage.

Basic Disks

When WS2003 is installed on a system, its disks are first configured to use basic storage. A disk that uses basic storage is called a basic disk. Basic disks are similar to disks in NT 4.0 and can consist of either:

Up to three primary partitions plus one extended partition. The extended partition can have up to 24 logical drives, and each primary partition and logical drive is identified by a unique drive letter from C to Z.
Up to four primary partitions and no extended partition or logical drives. Each partition is again identified by a unique drive letter.

Basic disks in WS2003 can be formatted using any of the following filesystems: FAT, FAT32, and NTFS. This is different from NT 4.0 Server, which supported only FAT and NTFS. The only real advantage of using basic storage is that you can dual-boot between WS2003 and legacy operating systems such as NT 4.0 Server or Windows 98something you are unlikely to do on real production servers, however. The disadvantages of basic disks are:

There is a limit of 4 primary partitions and 24 logical drives that you can create.
Configuration information concerning the disk is stored in the registry rather than on the disk itself. If the registry becomes corrupted, the data on the disk becomes unusable.
Basic disks in WS2003 can't be used to create the mirror sets, volume sets, stripe sets, and stripe sets with parity that you can create in NT. In order to use these advanced disk storage features, you must use dynamic storage instead of basic.

You can have mirror sets, volume sets, stripe sets, and stripe sets with parity on WS2003 systems using basic storage, but only if you upgraded the system from an earlier NT Server system that already had these storage technologies in place.

Dynamic Disks

WS2003 also supports a more advanced form of disk storage called dynamic storage. A disk that uses dynamic storage is called a dynamic disk. While basic disks contain partitions, dynamic disks contain volumes, and these volumes can be identified by either:

Associating a volume with a drive letter. However, this can be used only to identify up to 24 different volumes (or 25 if you have no B : floppy drive in your system).
Mounting a drive, which associates a volume with a folder on an existing volume. This method overcomes the drive-letter limitation and also enables friendly names like My Volume to be used to identify volumes.

The advantages of dynamic disks are:

There is no limit to the number of volumes you can create on a dynamic disk (other than hardware limitations).
Configuration information concerning the disk is stored on the disk instead of in the registry and is replicated to all other dynamic disks in the system for fault tolerance.
You can extend a simple volume on a dynamic disk by adding unallocated space to it from the same disk (you can't extend partitions on basic disks).
Dynamic disks support advanced disk technologies such as spanned, mirrored, striped, and RAID-5 volumes.

The disadvantage of dynamic disks is that you can't dual-boot between WS2003 and a legacy Windows operating system. Also, once you convert a disk to dynamic storage, you can't convert it back to basic without losing your data (unless you backed it up).

Advanced Disk Technologies

A volume is an area of storage on a dynamic disk, and a simple volume is a volume that occupies contiguous space on a single physical disk. Simple volumes are for dynamic storage as primary partitions and logical drives are for basic storage. Simple volumes can be extended with unallocated space from the same drive as long as they are formatted with NTFS. When extending a volume, WS2003 uses the smallest area of contiguous unallocated space it can find on the drive.

Other types of volumes supported by dynamic disks include:

Spanned volume: Created from two or more areas of contiguous free space on the same or on different physical disks that are combined into a single, larger, logical storage area. Spanned volumes can be extended without losing existing data by adding further areas of contiguous free space, up to a maximum of 32 areas and up to 32 different disks. However, once extended, they can't be reduced in size. Data is written to the first area of the volume until it becomes full, whereupon further data is written to the next area. Spanned volumes aren't fault-tolerant, and if one disk fails, the entire spanned volume is unrecoverable.
Striped volume (RAID-0): Created from two or more areas of contiguous free space on different physical disks that are combined into a single, larger, logical storage area. Like spanned volumes, striped volumes can consist of between 2 and 32 areas of contiguous free space. Unlike spanned volumes, however, each area of a striped volume must be on a different physical disk, all areas must be the same size, and data is written in an interleaved fashion across all areas instead of sequentially area by area. This generally provides better read performance than a spanned volume. Like spanned volumes, striped volumes are also not fault-tolerant.
Mirrored volume (RAID-1): A fault-tolerant technology that consists of two separate simple volumes that are configured to be identical copies of each other and are located on different physical disks. When data is updated on one disk, it is automatically updated on the other as well, and the pair of volumes is identified to the system by a single drive letter or mount point. If one disk in a mirrored volume fails, you still have the complete data on the other disk.
RAID-5 volume: Created from three or more areas of contiguous free disk space on different physical disks that are combined into a single, larger, logical storage area. RAID-5 volumes are similar to striped volumes, except that error-correcting parity information is distributed across the set. The result is a popular fault-tolerant disk storage technology called RAID-5, which maintains data integrity in the event of failure of a single physical disk belonging to the set. RAID-5 volumes can use between 3 and 32 different disks.

The advanced disk technologies supported by Windows 2003 are similar to those supported by NT 4.0 Server but are named differently, as shown in Table 4-8.

Table 4-8. Disk terminology in WS2003 and NT Server

NT	WS2003
Basic storage	Basic storage	Dynamic storage
Partition	Partition	Simple volume
Primary partition	Primary partition	Simple volume
Extended partition	Extended partition	N.A.
Logical drive	Logical drive	Simple volume
Mirror set	N.A.	Mirrored volume
Volume set	N.A.	Spanned volume
Stripe set	N.A.	Striped volume
Stripe set with parity	N.A.	RAID-5 volume

If you want to extend volumes or create striped, spanned, or fault-tolerant volumes, you first have to convert your disks from basic to dynamic storage. You can convert your disks without rebooting the systemunless the disk contains your system or boot partition or the active paging file.

To convert them to dynamic disks, basic disks must have a minimum of 1 MB of free space. This free space is used to store the database containing the configuration information concerning all the dynamic disks in the system. When you partition a basic disk, make sure you leave at least 1 MB of free (unallocated) space on the disk in case you later want to convert it to dynamic storage.

The conversion of a disk from basic to dynamic storage should take place with no loss of data on the disk, but, to be safe, you should always back up a basic disk before converting it to dynamic.

Disk Quotas

Disk quotas manage the amount of disk space that users can utilize. Quotas are available only on NTFS partitions or volumes. Disk quotas can be configured several ways:

Quota limits can be either enforced or not. If enforced, users who exceed their limits are denied access.
Warnings can be issued when a user is nearing the configured quota limit.
An entry can be logged in the event log when a warning is issued, when a limit is exceeded, or both.

Disk quota limits are based on file ownership and not on where the files are located on a quota-enabled NTFS volume; that is, they are established on a per-user basis. For example, if a user moves a file from one folder to another on the volume, she still shows the same amount of disk space used in My Computer or Windows Explorer. If a user takes ownership of a file on an NTFS volume, the file is charged against the user's quota.

In addition, disk quotas apply only to specific volumes and not to folders within volumesthat is, on a per-volume basis. If a physical disk has several volumes or partitions (or if you have multiple physical disks), each partition or volume may have quotas either enabled or disabled, and those on which quotas are enabled may have different quota limits set (unless it's a spanned volume).

Quota Limits

Disk quota limits can be one of two types:

Soft quotas: When the user exceeds the limit, an event may be logged to the event log, but the user is not prevented from exceeding the quota.
Hard quotas: When the user exceeds the limit, an event may be logged to the event log, and the user is prevented from using any additional space on the disk.

Once enabled on a volume, disk quota limits are tracked for all users who store files on that volume. However, different quota limits can be set for specific users to override the global settings for all users. Once quota limits have been established on a volume, users are monitored for any action that increases the amount of disk space used. These actions include:

Copying or moving files to the disk
Creating (saving) new files on the disk
Taking ownership of existing files on the disk that belong to other users

User applications may respond differently when users try to create or save files on volumes on which a hard quota limit has been exceeded. In general, applications act as if the volume is full.

Implementing Disk Quotas

Begin by establishing realistic estimates of how much disk space users require on average and how these needs are likely to grow in the immediate future. To do this, you may want to classify users into three different categories, such as heavy users, moderate users, and light users.
Next, create partitions, volumes, and logical drives in such a way as to facilitate assigning space to different types of users. Allocate some volumes for heavy users, some for moderate, and some for light. Create home folders or data folders on these drives for each user or group of users, and assign NTFS permissions accordingly to restrict access. Make sure you leave unallocated space on the drives in case you need to increase the quota limits. Consider using dynamic storage so that you can extend simple volumes and create spanned volumes when simple volumes become full.
Assign disk quotas to each volume, partition, or logical drive according to the type of user storing data there. Use soft limits initially in case your estimates of user needs are too small.
Now share the folders for access over the network. Closely monitor disk quota entries over a period of time to see if realistic limits have been set.
Once you have determined that your quota limits are appropriate, make them hard quotas to prevent careless users from overutilizing disk space.
Monitor quotas periodically to determine whether they should be increased for all users. Check whether specific users might require individual quotas for special projects and so on.
If a user no longer needs to store data on a volume, remove the files (or take ownership of them) and then delete the user's quota entry to free up space on the volume.

Make sure you enable quotas on a disk before any users have stored files on it. If a user has already stored a file and you then enable quotas and set quota limits, the user's quota limit is No Limit and you will have to change the quota entry manually for this user. Only new users who later store files on the disk are assigned the quota limits you expect them to have.