DISK STATISTICS

[Hemant_7]

Hi
How to get the disk statistics of the devices same as v get through "sar -d 1 10" command . Actually i want to write a C funtion which give me all the details like device , %busy, avque, r+w/s, blks/s avwait , avserv.
Is there any structure in HPUX that gives all this information ??. If it is how to get info from it ??
The reason i cant use because sar command its not giving all the details of all the disk attached to the system.
Because if i c "/dev/dsk" directory there r 4 devices attached and sar is giving me only detail of 2.

Waiting for ur reply
hemant

[Paula J Frazer-Campbell]

Hi

Sar -d will only give statistics on disks that have activity, so getting the %busy, avque, r+w/s, blks/s avwait , avserv on non active disks will result in nul/no activity results.

Because the disks do not appear in the sar -d output therefore does not mean that sar is incorrect, just that they are not in use at the time that sar was collecting data.


Paula

[Dietmar Konermann]

Hi!

The sar command uses the pstat(2) interface to get that information. In your case you should have a look at pstat_getdisk().

There are also examples in the man page.

Regards...
Dietmar.

[Hemant_7]

Hi
Thanks for the reply .I tried using the pstat_getdisk function . But struct pst_diskinfo has no information about "device %busy , avque, r+w/s, blks/s , avwait , avserv " field . Please correct me if i m wrong !

thanks
hemant

[Dietmar Konermann · Accepted solution]

You are right... the metrics are not directly available. They need to be calculated.

Most of them are cumulative values... so you need to take 2 samples, get the differences then do some maths with it.

E.g.:

avwait = ( ( (float)DEV_DIFF_USEC(psd_dkwait) ) / 1000.0 ) /
(float)DEV_DIFF(psd_dkq_merged);

avserv = ( ( (float)DEV_DIFF_USEC(psd_dkresp) ) -
( (float)DEV_DIFF_USEC(psd_dkwait) ) );

So it's not trivial...

Regards...
Dietmar.

[Hemant_7]

Hi there
Thats really a great ! thanks a lot for it !

Could u please tell me the algo for the %bsy and avque r+w/s field also . How to calculate it ?? . Where i can find this info for calculating it....

One more thing pstat_getdisk sycall , return the number of disk attached to the system is this true ??.

waiting for ur reply
thanks and regard
hemant

[Dietmar Konermann]

Hi, Hermant!

The formulas are not documented explicitely... however, one may derive them from performance tuning guides. So it's not a big secret. :)

Here we are:

busy_percent = MAX( (float) DEV_DIFF (psd_dktime) / delta_time * 100.0 , 100 );

avque = (float)DEV_DIFF(psd_dkqlen) / (float)DEV_DIFF(psd_dkq_merged) -1;

rw = (float) DEV_DEV_DIFF(psd_dkq_merged) / delta_time * 100;

(delta_time is in ticks... 100 ticks/sec).

The syscall returns the number of structs it filled to buf. So it's:

MIN (#disks, elemcount)

Regards...
Dietmar.