1 08/16/84 tune_disk, td
2
3 Syntax: tune_disk drive_name io_type -load | -ld n
4 -response | -rsp m
5 tune_disk reset_max
6 tune_disk reset_sys
7 tune_disk stagnate seconds
8 tune_disk system io_type -max n -map io_type
9
10 Function: Permits a user with hphcs_ access to alter disk tuning
11 parameters.
12
13
14 Arguments:
15 io_type
16 An io_type is the name of a type of IO tunable by tune_disk.
17 If tune_disk is envoked without arguments it will print a
18 usage message which includes the valid io_type names.
19
20 drive_name
21 Is the name of a disk drive to be tuned. Drive names must
22 begin with the three characters "dsk", followed by a letter,
23 an underline and one or two numeric digits.
24
25 -load n, -ld n
26 This argument pair defines the optimization maximum queue
27 loadpoint for the specified drive. It is one of the two
28 points which define the optimization line. If -load 1 is
29 specified, the initial response value is the optimizing
30 multiplier and no load optimization is performed.
31
32
33 -response m, -rsp m
34 This argument pair defines the optimization maximum response
35 value, which is the multiplier to be used for an IO type queue
36 load of a single request.
37
38 reset_max
39 This argument requests that all queue maximum depth meters be
40 reset in the disk_seg database. The time and date at which
41 the meters were last reset is also maintained in the database.
42 This argument is useful to permit a new/lower max depth to be
43 seen after altering tuning parameters, or after an Allocation
44 Lock has occurred.
45
46
47 reset_sys
48 This argument requests that all system depth counters be reset
49 to 0. This is useful after altering system depth counter
50 mapping. If counter mapping has been changed while requests
51 were in the queue, the counter which had been used may be left
52 artificially high. Resetting back to 0 lets the system
53 correct the value.
54
55 stagnate seconds
56 This argument pair specifies a change of the system wide
57 stagnation time period to the specified number of seconds.
58 Tune_disk sets a maximum stagnation time period of 6 minutes.
59
60
61 system
62 This argument indicates modification of a system-wide
63 optimization factor. The maximum depth and/or mapping for the
64 specified io_type will be altered. If neither a maximum depth
65 value, nor a mapping is altered an error message is issued.
66
67 -map io_type
68 This argument specifies that the current depth counting for
69 the specified system-wide optimization entry should be done
70 using the counter for io_type. For example:
71
72 tune_disk system PageRead -map PageWrite
73
74 Would have the depth counter for PageWrite used to accumulate
75 the number of PageRead IO's currently outstanding.
76
77
78 -max n
79 This argument pair indicates that the maximum depth for the
80 specified system-wide optimization entry should be set to n.
81 If this depth is reached then full optimization of this IO
82 type will be done system wide for all drives.
83
84
85 Notes:
86 Optimization is performed by determining a multiplier to be
87 used to convert a Phsical Seek Length into a Logical Seek
88 Length, for the purposes of determining the Nearest Logical
89 Seek to perform on a disk drive. The Response Point
90 determines what this multiplier is for a situation with a
91 single request of that IO type in the queue, and is the
92 multiplier required to produce best system response. The Load
93 Point specifies the number of requests permitted in the queue
94 of the specified IO type before full optimization occurs,
95 Logical Seek Length = Physical Seek Length. These two values
96 define the two endpoints of a straight line. The optimization
97 multiplier is determined by the current load of the queue and
98 its corresponding position on the straight line.
99
100
101 System-wide queue loading optimization is determined by
102 looking at the system-wide load of an IO type and the maximum
103 depth it should be permitted before becoming fully optimized.
104 The fraction produced by:
105
106 fraction = max 0.0 max_depth - depth/max_depth
107
108 is used to alter the individual drive's IO type multiplier to
109 determine the system-wide queue loading effect on individual
110 drive optimization.
111
112
113 The system-wide optimization utilizes a max_depth specified
114 for the IO type, and a counter of the current depth to
115 determine the system-wide loading optimization. Depth
116 counters can be mapped together to form an aggregate
117 system-wide queue loading effect. When decrementing, counters
118 are not permitted to become negative, but if re-mapped while
119 non-zero they may remain > 0 with no load. The tuning tools
120 permit resetting the current depth counters for system-wide
121 optimization back to 0, to let the system correct them to a
122 true load indication.
123
124 All queues have a high-water-mark accumulator. This can be
125 reset through the tuning tools to permit a new high-water-mark
126 to be determined.