disk performance

[Steven Pao]

We found that there are 2 disks (c0t0d5, c0t2d0) loading very heavy in
our daily process. Would you please kindly check for us if there is any
problem in them, especially c0t0d5?

The following is disk performance log, FYI. And you would see the
busy percentage (%busy) of c0t0d5 is always much higher than others. I
wonder if there is any possibility except data is allocated in it.
(See attached file: sard.log)

[Michael Tully]

Hi Steven,

Please advise what is running on this particular disk compared to the
others, application(s) etc, what disk has the operating system
on it?

What types of disk are these, internal ??

Michael....

[Steven Pao]

Hi Michael,

HP K370
HP-UX 10.20
EMC 3330 External disk array
c0t0d0~c0t0d5 (9GB raid-5 VOLUMES * 6 = 54GB)
c0t1d0~c0t1d2 (9GB raid-5 VOLUMES * 3 = 27GB)
c0t2d0~c0t2d2 (18GB raid-5 VOLUMES * 4 = 54GB)

[Ravi_8]

hi,
provide the more information about which os,applications,RAM, what u have in each mentioned disks. as we can't physically see the disks, the information what u gives is the source to diagonise problem

later
ravi

[Paula J Frazer-Campbell]

Hi
As this disk is your data disk it is normal to see it busier that other disks as it is being read from and written to.

Its %busy it a good indication as to what is happening and its peak times will help point you to what is making it busy.

I have disks on my main server which are being used by over 600 users and will sit above 80% for 10 min plus during the day, providing that avwait does not get to high I do not worry, but monitor.

So a busy disk is relative ? what you see as busy on your system will be a quiet one on a different system.

So yes it is busier, but not excessively so.

Have look at the peak %busy times and attribute them to activity.
Can this activity be spread out?
Grep out that disk and graph its activity over the day:-
Sar ?d |grep c0t0d5 >diskbusy
Pull the diskbusy file into something like excel and graph its activity.

I have enclosed an example excel spreadsheet.

HTH

Paula

[Stefan Farrelly]

I dont think you have anything to worry about. Your disk c0t5d0 running around several % busy is not very heavy at all. Its probably your boot disk anyway, thus it will be busier than your other disks. From the lvlnboot -v command is c0t5d0 your boot disk ?

Here are some sar stats from one of our boxes;

10:22:24 device %busy avque r+w/s blks/s avwait avserv
10:22:26 c0t6d0 28.43 0.50 32 425 6.02 22.66
c0t5d0 24.51 0.50 29 402 5.23 17.45
c5t0d0 0.98 0.50 3 47 2.61 4.46
c6t5d0 0.98 0.50 2 31 4.70 4.27
10:22:27 c0t6d0 4.04 0.50 4 40 2.08 14.96
c0t5d0 3.03 0.50 2 32 2.45 19.20
c5t9d0 1.01 0.50 1 16 2.53 10.46
c5t2d0 1.01 0.50 1 16 2.08 8.85
10:22:28 c0t6d0 4.00 0.50 4 60 4.21 7.66
c0t5d0 4.00 0.50 4 60 4.25 7.41
c0t8d0 2.00 0.50 2 32 0.85 16.71
c5t11d0 1.00 0.50 1 16 3.08 12.66
c6t5d0 1.00 0.50 3 48 6.18 3.39
10:22:29 c0t6d0 8.00 0.50 8 76 6.30 28.88
c0t5d0 6.00 0.50 6 68 8.07 26.32

Average c0t6d0 10.18 0.50 11 137 5.59 19.81
Average c0t5d0 8.98 0.50 10 126 5.45 16.29

As you can see from this, c0t6d0 and c0t5d0 are our vg00 disks (c0t6d0 is the boot disk) and theyre running busier than yours, but perfromance for us on the server is fine.

[Ovidiu D. Raita]

The load on the disk is very low. Nothing to warry about. If you face performance problems it's not because of the disks.

Ovidiu

[Ferrety Frederick]

Hi,

Yes, I think you have a performance problem.
The bad metric is not the busy%.
The problem came from the avque avwait avserv.
The avque: your disk can't handle the io requested by the system, so there are queued! the perf impact is major (good value < 0.5 )
The avwait and avserv are too high (good value are avwait<6 and avserv<1.
To see the time wasted in io waiting (sar -Mu)
To investigate:
1 - Your EMC physical disk raid group is over loaded by and other system or an parity disk !
2 - Your disk access is highly random access, so you disk is speeding lot of time in head moving ( look emc physical disk seek time and hit ratio for this disk :it could divide perf by 10)
EMC tools (ECC) or EMC support should help you.

Good luck,

Frederick