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Understanding Clusters, Sectors, and Wastage in File Storage Details

Explore the definitions of sectors, clusters, and wastage in file storage systems. Learn about cluster sizes, NTFS and FAT32 handling, common cluster sizes, and examples illustrating wastage. Gain insights on maximizing disk space usage and minimizing wastage.

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Understanding Clusters, Sectors, and Wastage in File Storage Details

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  1. Clusters, Sectors, and Wastage More File Storage Details CSCI 325

  2. Recap - Definitions • Sector • sector size determined by HDD manufacturer • size is almost always 512 bytes • commonly 63 sectors per track • hence, a common track size is 31.5 KB • Cluster • a group of sectors • the smallest unit of disk space manageable by the Operating System • files use whole clusters • hence, some wastage; hence today's lecture

  3. Recap -Effect of Cluster Sizes • NTFS • NTFS-5 handles max 264 clusters • Max Disk Size • with 4K clusters = 16 TB • with 64K clusters = 256 TB • FAT32 • Max Disk Size • with 32K clusters = 8TB • with .5K clusters = 2TB

  4. Common Cluster Sizes • Cluster sizes (sectors per cluster) are always powers of 2. • Cluster size is fixed at disk format time. • Default cluster sizes for NTFS: http://support.microsoft.com/kb/140365

  5. Example Stolen from Dr. Foster's CSCI325 Course Notes Wastage - Example 1 File Size = 100,000 bytes Cluster Size = 8 sectors 100000 bytes clusters needed = ------------------------------------- 8 sectors/cluster * 512 bytes/sectors 100000B --------------- = 24.41 clusters = 25 clusters 4096B/cluster Allocated Space = 25 clusters * 4096B/cluster = 102400Bytes not used 2400B Percent Wastage = --------- = ------- = 2.34% allocated 102400B

  6. Wastage - Example 2 File Size = 100,000 bytes Cluster Size = 1 sector 100000B clusters needed = ------------ = 195.31 = 196 clusters 512B/cluster Allocated Space = 196 clusters * 512B/cluster = 100352Bytes 352B Percent Wastage = --------- = 0.35% 100352B

  7. Example Stolen from Dr. Foster's CSCI325 Course Notes Wastage - Example 3 File Size = 30 bytes Cluster Size = 8 sectors 30B clusters needed = --------------- = 1 cluster 4096B/cluster Allocated Space = 1 cluster * 4096B/cluster = 4096Bytes 4066B Percent Wastage = -------- = 99.27% 4096B Small Files in Big Clusters = Lots of Wasted Space

  8. Wastage - Example 4 File Size = 30 bytes Cluster Size = 1 sector 30B clusters needed = -------------- = 1 cluster 512B/cluster Allocated Space = 1 cluster * 512B/cluster = 512Bytes 482B Percent Wastage = -------- = 94.14% 512B

  9. Wastage - Example 5 Size of this PowerPoint file = 92,817 bytes Cluster Size on my office's WindowsXP = 4KB (8 sectors) 92817B clusters needed = --------------- = 22.66 = 23 clusters 4096B/cluster Allocated Space = 23 cluster * 4096B/cluster = 94208Bytes 1391B Percent Wastage = -------- = 1.48% 94208B See Next Page

  10. File Properties • Usage = 90.6KB / 92.0KB = 98.48% • Wastage = 100% - 98.48% = 1.52% Size Allocated Space

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