The following are examples of seeksize.d. seeksize.d records disk head seek size for each operation by process. This allows up to identify processes that are causing "random" disk access and those causing "sequential" disk access. It is desirable for processes to be accesing the disks in large sequential operations. By using seeksize.d and bitesize.d we can identify this behaviour. In this example we read through a large file by copying it to a remote server. Most of the seek sizes are zero, indicating sequential access - and we would expect good performance from the disks under these conditions, # ./seeksize.d Sampling... Hit Ctrl-C to end. ^C 22349 scp /dl/sol-10-b63-x86-v1.iso mars: value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 726 1 | 0 2 | 0 4 | 0 8 |@ 13 16 | 4 32 | 0 64 | 0 128 | 2 256 | 3 512 | 4 1024 | 4 2048 | 3 4096 | 0 8192 | 3 16384 | 0 32768 | 1 65536 | 0 In this example we run find. The disk operations are fairly scattered, as illustrated below by the volume of non sequential reads, # ./seeksize.d Sampling... Hit Ctrl-C to end. ^C 22399 find /var/sadm/pkg/ value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@@@@ 1475 1 | 0 2 | 44 4 |@ 77 8 |@@@ 286 16 |@@ 191 32 |@ 154 64 |@@ 173 128 |@@ 179 256 |@@ 201 512 |@@ 186 1024 |@@ 236 2048 |@@ 201 4096 |@@ 274 8192 |@@ 243 16384 |@ 154 32768 |@ 113 65536 |@@ 182 131072 |@ 81 262144 | 0 I found the following interesting. This time I gzipp'd the large file. While zipping, the process is reading from one location and writing to another. One might expect that as the program toggles between reading from one location and writing to another, that often the distance would be the same (depending on where UFS puts the new file), # ./seeksize.d Sampling... Hit Ctrl-C to end. ^C 22368 gzip sol-10-b63-x86-v1.iso value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@@@ 353 1 | 0 2 | 0 4 | 0 8 | 7 16 | 4 32 | 2 64 | 4 128 | 14 256 | 3 512 | 3 1024 | 5 2048 | 1 4096 | 0 8192 | 3 16384 | 1 32768 | 1 65536 | 1 131072 | 1 262144 |@@@@@@@@ 249 524288 | 1 1048576 | 2 2097152 | 1 4194304 | 2 8388608 |@@@@@@@@@@@@@@@@@@ 536 16777216 | 0 The following example compares the operation of "find" with "tar". Both are reading from the same location, and we would expect that both programs would generally need to do the same number of seeks to navigate the direttory tree (depending on caching); and tar causing extra operations as it reads the file contents as well, # ./seeksize.d Sampling... Hit Ctrl-C to end. ^C PID CMD 22278 find /etc value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@@@@@@@@@@@ 251 1 | 0 2 |@ 8 4 | 5 8 |@ 10 16 |@ 10 32 |@ 10 64 |@ 9 128 |@ 11 256 |@ 14 512 |@@ 20 1024 |@ 10 2048 | 6 4096 |@ 7 8192 |@ 10 16384 |@ 16 32768 |@@ 21 65536 |@@ 28 131072 |@ 7 262144 |@ 14 524288 | 6 1048576 |@ 15 2097152 |@ 7 4194304 | 0 22282 tar cf /dev/null /etc value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@ 397 1 | 0 2 | 8 4 | 14 8 | 16 16 |@ 24 32 |@ 29 64 |@@ 99 128 |@@ 73 256 |@@ 78 512 |@@@ 109 1024 |@@ 62 2048 |@@ 69 4096 |@@ 73 8192 |@@@ 113 16384 |@@ 81 32768 |@@@ 111 65536 |@@@ 108 131072 |@ 49 262144 |@ 33 524288 | 20 1048576 | 13 2097152 | 7 4194304 | 5 8388608 |@ 30 16777216 | 0