Monitoring Disk Space

It is important to monitor the amount of available storage space on your disk because programs might fail due to an inability to allocate space. In addition, low disk space might make it impossible for your paging file to grow to support virtual memory. Fragmentation also has this effect. For information about setting the paging file size for optimal performance, see "Evaluating Memory and Cache Usage" in this book.

Use the % Free Space and Free Megabytes counters to monitor disk space. If the available space is becoming low, you might want to run Disk Cleanup in the Disk Properties dialog box, compress the disk, or move some files to other disks. Notice that disk compression incurs some performance loss.

Another option is Remote Storage, which enables you to create virtual disk storage out of tape or optical drives. When you use this service, infrequently accessed files are moved to tape or to other media storage. Remote Storage volumes are well suited for data that you need to access only at certain intervals, such as quarterly reports. For more information about remote storage options, see "Data Storage and Management" in this book.

If you are using NTFS and you want to restrict the amount of space allocated by individual users, use the Quota tab in Disk Properties. Notice that using quotas results in a small performance loss. If you are not using NTFS, you can set an alert on the % Free Space counter to track dwindling disk space.

Note

Free space on a Distributed file system (Dfs) share can change as you move from one directory to another within a Dfs share namespace. Thus, when accessing network shares, do not assume that the amount of free space you see at the root is available throughout the entire tree.

Even if you are not currently short on disk space, you need to be aware of the storage requirements for applications you are running. Complete the following procedure to determine whether your disk has adequate space for your needs.

To evaluate the adequacy of your system's disk capacity

1. For best results, start with 1 GB (although the minimum disk size required to install the operating system might be lower).
2. Add the total size of all applications.
3. Add the size of the paging file (this depends on the amount of memory; this size should be at least twice that of system memory).
4. Add the amount of disk space budgeted per user (if a multiuser system), multiplied by the number of users.
5. Multiply by 130 percent to allow room for expansion (this percentage can vary based on your expected growth).

The result is the size of disk you need.

Note

Although not exactly a disk-storage issue, disk fragmentation slows the transfer rate and seek times of your disk system and you should monitor for increasing disk fragmentation. On single-disk systems, you can use the Split IO/sec counter to determine the degree of fragmentation of your disks. Defragment the disk if this counter rate is consistently high and run Disk Defragmenter periodically to keep stored data organized for best performance.

Figure 8.2 shows a graph of disk counters including % Free Space. Notice that the % Free Space counter begins to rise approximately halfway through the graph. This illustration shows changes that result from deleting files on the disk.

Enlarge figure

Figure 8.2 Increase in % Free Space Counter

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