Windows 8 : Managing Disk Drives and File Systems - Working with Basic and Dynamic Disks

Not that long ago, all Windows computers shipped with their hard disks configured as basic disks. Now, because people want larger or more robust disks, computer manufacturers have responded by shipping more computers with their hard disks configured as dynamic disks. Instead of having a single 500-GB drive, a new computer might have a spanned disk with 1,000 GB, where two 500-GB physical drives act as a single logical disk. In this scenario, disk spanning is used to make multiple disks appear to be a single disk. One way to implement this on Windows 8 is to use dynamic disks.

As more and more computers are shipped with dynamic disks, you might wonder whether your computers that use basic disks should be converted to dynamic disks. In some cases, the need for standardization might prompt your decision. For example, for better manageability, you might want all desktops in a particular department to have the same configuration. In other cases, IT management might direct the change because the conversion from basic disks to dynamic disks can be considered an upgrade process. (That is, you are moving computers from an older disk type to a newer disk type.) However, before you decide to move from one disk type to another, you should understand what is involved, what features are supported, and what features are not supported.

A basic disk is a physical disk that has one or more basic volumes that can be configured as primary partitions, plus an optional extended partition consisting of logical drives. A primary partition is a drive section that you can access directly for file storage. Each physical drive can have up to four primary partitions. You make a primary partition accessible to users by creating a file system on it. In place of one of the four permitted primary partitions, you can create an extended partition (meaning that the basic disk could have up to three primary partitions and one extended partition). Unlike with primary partitions, you can’t access extended partitions directly. Instead, you can configure extended partitions with one or more logical drives that are used to store files. Being able to divide extended partitions into logical drives enables you to divide a physical drive into more than four sections. For example, you could create logical drives F, G, and H in a single extended partition.

A dynamic disk is a physical disk that has one or more dynamic volumes. Unlike a basic disk, a dynamic disk can have an unlimited number of volumes—any one of which can be extended or used as a system volume. Although basic disks can be used with any Windows-based operating system, dynamic disks can be used only with Windows 2000 or later releases.

A key advantage of dynamic disks used to be their ability to combine physical disks using the spanning, striping, or mirroring features of Windows. However, Windows 8 allows you to span, stripe, or mirror basic disks as well. When you span or stripe drives, you create a single volume that extends from one disk to other disks, using all or part of each disk in the set. The difference between spanning and striping is how data is written. Windows 8 recognizes spanned disks in the same way it would a single partition, and write operations to the spanned disk are made to the entire partition randomly. With striping, Windows 8 writes a portion of the data to each of the underlying disks that make up the volume. In most cases, striping gives you faster read/write access to data because data is read from and written to multiple disks. With mirroring, two drives are combined to create a single fault-tolerant volume. If any one volume fails, the other volume in the set is still available, and the volume can be recovered.

Now, because you can span, stripe, and mirror drives using the basic disk type, the key features that distinguish dynamic disks from basic disks are enhanced error correction and detection and the ability to modify disks without having to restart the computer. Other features available on a disk depend on the disk formatting, such as whether you are using exFAT or NTFS.

When you format a disk with a file system, the file system structures the disk using clusters, which are logical groupings of sectors. With 512b drives, FAT, FAT32, exFAT, and NTFS use a fixed sector size of 512 bytes but allow the cluster size to be variable. For example, the cluster size might be 4,096 bytes, so if there are 512 bytes per sector, each cluster is made up of eight sectors.

Table 1 provides a summary of the default cluster sizes for FAT16, FAT32, exFAT, and NTFS. You have the option of specifying the cluster size when you create a file system on a disk, or you can accept the default cluster-size setting. Either way, the cluster sizes available depend on the type of file system you are using.

The important thing to know about clusters is that they are the smallest unit in which disk space is allocated. Each cluster can hold one file at most. So, if you create a 1-KB file and the cluster size is 4 KB, there will be 3 KB of empty space in the cluster that isn’t available to other files. That’s just the way it is. If a single cluster isn’t big enough to hold an entire file, the remaining file data goes into the next available cluster and then the next, until the file is completely stored. For FAT, for example, the first cluster used by the file has a pointer to the second cluster, and the second cluster has a pointer to the next, and so on until you get to the final cluster used by the file, which has an end-of-file (EOF) marker.

The disk I/O subsystem manages the physical structure of disks. Windows manages the logical disk structure at the file system level. The logical structure of a disk relates to the basic or dynamic volumes you create on a disk and the file systems with which those volumes are formatted. You can format both basic volumes and dynamic volumes using FAT or NTFS. Each file system type has a different structure, and there are advantages and disadvantages of each as well.

Although you can use both basic and dynamic disks on the same computer, the disks that make up a volume must use the same disk type. Remember that although you can convert the disk type from basic to dynamic and preserve the data on the disk, you must delete any existing partitioning on a dynamic disk before you can convert from dynamic to basic. Deleting the partitioning destroys any data on the associated disks. Finally, dynamic disks cannot be created on any removable-media drives or on any disk on a portable computer. Laptops, Tablet PCs, and other types of portable computers can have only basic disks.