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Clusters, Sectors, and Wastage

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

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Clusters, Sectors, and Wastage

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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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