To determine if fragmentation will occur as new files are created, examine the Free Storage Utilization section of the Disk Space report. Look at the free storage extent size closest to 80%. Now examine the Allocated Space Utilization section of the Disk Space report. Look at the allocated extent size closest to 80%. If the size of most space allocated (files created) is smaller than most free storage size (space available), little or no fragmentation is likely to occur on that disk. If the size of most files created is larger than the free extent size, fragmentation may occur as new files are created.
In the following example, in the 82.5 percentile, free storage extent sizes range from 900 to 1500 blocks. In the example labeled “Allocated Space Utilization - Report Example”, in the 84.6 percentile, allocated extent sizes range from 60 to 90 blocks. Therefore, the size of free storage is more than enough to accommodate the new files as they are created, and disk fragmentation is not likely to occur if future disk usage follows current usage.
Disk Analysis _NUN$DUA32: (COOLER) Page 1 Summary of Free Storage Performance Agent VX.X Monday 11-MAY-2008 14:50 Free Storage Extent Sizes No. Extents Cum % Space -------------------------- ----------- ----------- >= 3, < 6 201 1.3 >= 6, < 9 88 2.4 >= 9, < 15 91 4.5 >= 15, < 30 110 9.2 >= 30, < 60 80 16.0 >= 60, < 90 42 22.5 >= 90, < 150 22 27.8 >= 150, < 300 36 43.6 >= 300, < 600 16 57.8 >= 600, < 900 10 74.4 >= 900, < 1500 3 82.5 >= 1500, < 3000 2 91.0 >= 3000, < 6000 1 100.0 >= 6000, < 9000 0 100.0 >= 9000, < 15000 0 100.0 >= 15000, < 30000 0 100.0 >= 30000, < 60000 0 100.0 >= 60000, < 90000 0 100.0 >= 90000, < 150000 0 100.0 >= 150000 0 100.0 Total free blocks = 46284. No. of extents = 702. Mean blocks/extent = 66. Smallest extent = 3. Largest extent = 4158.
To evaluate file fragmentation, examine the Allocated Space section of the Disk Space report. Look at the number of extents allocated, the total number of files, and the mean number of extents per file. A value of 1 for mean number of extents per file indicates that most files have only one extent; therefore, they are not fragmented. A disk with a small number of files and a large number of extents per file indicates that the files are fragmented. In the following example, the mean number of extents per file is 2 and there are a large number (10052) of small files, indicating that these files may be fragmented.
In some cases, it may not be necessary to use the BACKUP utility on a disk. If a heavily used file has more than one extension header and appears to be the source of the device's bottleneck, copying the file to a contiguous area may be sufficient to improve performance.
Disk Analysis _NUN$DUA32: (COOLER) Page 3 Summary of Allocated Space Performance Agent VX.X Monday 11-MAY-2008 14:50 Space Allocated per Header No. Headers Cum % Headers -------------------------- ----------- ------------- >= 3, < 6 2979 29.7 >= 6, < 9 1162 41.2 >= 9, < 15 1116 52.3 >= 15, < 30 1423 66.5 >= 30, < 60 1296 79.4 >= 60, < 90 522 84.6 >= 90, < 150 742 92.0 >= 150, < 300 448 96.4 >= 300, < 600 202 98.5 >= 600, < 900 34 98.8 >= 900, < 1500 37 99.2 >= 1500, < 3000 44 99.6 >= 3000, < 6000 18 99.8 >= 6000, < 9000 12 99.9 >= 9000, < 15000 7 100.0 >= 15000, < 30000 3 100.0 >= 30000, < 60000 0 100.0 >= 60000, < 90000 0 100.0 >= 90000, < 150000 0 100.0 >= 150000 0 100.0 Minimum allocated extent = 3. Maximum allocated extent = 19191. Total allocated blocks = 844731 ( 94.8% of volume). Total used blocks = 777058 ( 92.0% of allocated). No. extents allocated = 18333. Mean alloc blocks/extent = 46. Total no. of files = 10052. Mean alloc blocks/file = 84. Mean no. extents/file = 2. No. extension headers = 26. No. multi-volume files = 0. No. directories = 435.
To further determine if a disk is fragmented, look at the number of extension headers in the Allocated Space section of the Disk Space report. When the number of extension headers is nonzero, there are one or more seriously fragmented files. A single header holds about 80 extent pointers; therefore, a file that needs an extension header is severely fragmented. In the preceding example, there are 26 extension headers, which indicates this disk is heavily fragmented.
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