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root/i-scream/projects/libstatgrab/docs/diskio.txt
Revision: 1.2
Committed: Thu Jun 5 16:02:43 2003 UTC (20 years, 11 months ago) by tdb
Content type: text/plain
Branch: MAIN
Changes since 1.1: +47 -28 lines
Log Message:
Proof read and slightly alter diskio.txt and network.txt. Also add
diskio.txt to the Makefile.

File Contents

# Content
1 DiskIO Statistics
2 =================
3
4 Data Structure
5 --------------
6
7 All diskio statistics return a structure of type diskio_stat_t that
8 looks like this:
9
10 typedef struct{
11 char *disk_name;
12 long long read_bytes;
13 long long write_bytes;
14 time_t systime;
15 }diskio_stat_t;
16
17 disk_name is the name known to the operating system.
18 (eg. on linux it might be hda)
19 read_bytes is the number of bytes that disk has read.
20 write_bytes is the number of bytes that disk has written.
21 sysname is the time period over which read_bytes and
22 write_bytes were transferred.
23
24 Functions
25 ---------
26
27 diskio_stat_t *get_diskio_stats(int *entries);
28
29 diskio_stat_t *get_diskio_stats_diff(int *entries);
30
31 Both calls take a pointer to an int, "entries", which is filled with
32 the number of disks the machine has. This is needed to know how many
33 diskio_stat_t structures have been returned. A pointer is returned to
34 the first diskio_stat_t.
35
36 get_diskio_stats returns the disk IO stored in the kernel which holds
37 the amount of data transferred since bootup. On some platforms, such as
38 Solaris 7, this value is stored in a 32bit int, so wraps around when it
39 reaches 4GB. Other platforms, such as Solaris 8, hold the value in a
40 64bit int, which wraps somewhere near 17 million terabytes.
41
42 get_diskio_stats_diff is the same as get_diskio_stats except it will
43 return the difference since the last call. So, for instance a call to
44 get_diskio_stats_diff is made, and called again 5 seconds later. Over
45 that time, 2000 bytes of traffic were written and 10000 bytes read.
46 write_bytes will store 2000 bytes, read_bytes will store 10000, and
47 systime will store 5. This function copes with wrap arounds by the O/S
48 so should be seemless to use.
49
50 Bugs
51 ----
52
53 On the very first call get_diskio_stats_diff will return the same as
54 get_diskio_stats. After the first call it will always return the
55 difference.
56
57 On operating systems that hold only 32bits of data there is a problem
58 if the values wrap twice. For example, on Solaris 7 if 9GB is
59 transferred and the operating system wraps at 4GB, the
60 get_diskio_stats_diff function will return 5GB.
61
62 Example
63 -------
64
65 A very basic example can be found in examples/disk_traffic.c