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Poor perfromance after breaking and removing mirror root disk???

 
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Poor perfromance after breaking and removing mirror root disk???

After breaking root mirror the system (at least vg00) is very sluggish. I noticed when running a sar -v it still shows the drive that was removed (c1t2d0) and shows it with values. Can anyone explain?

NOTE: ioscan shows NO_HW, as it should


#sar -v 3 3
07:50:26 device ~ %busy avwait avserv
07:50:29 c1t2d0 ~ 98.33 0.00 323.57 <--
c1t0d0 ~ 98.33 0.00 2608.15
~
~
07:50:32 c1t2d0 ~ 100.00 0.00 294.84
c1t0d0 ~ 100.00 0.00 3118.64
c2t2d0 ~ 0.33 0.01 6.79
~
~
07:50:35 c1t2d0 ~ 98.33 0.00 294.84
c1t0d0 ~ 98.33 0.00 2562.44
~
~
Average c1t2d0 ~ 101.44 0.00 304.10
Average c1t0d0 ~ 101.44 0.00 2760.54
6 REPLIES

Re: Poor perfromance after breaking and removing mirror root disk???

Sorry about the format issue on the sar output.

The Average: %busy on the removed drive is 98.33, await is 0.00 and the avserv is 304.10
Patrick Wallek
Honored Contributor
Solution

Re: Poor perfromance after breaking and removing mirror root disk???

>>After breaking root mirror...

How did you do this? Did you do an 'lvreduce' to reduce the mirrors off of the disk, followed by a 'vgreduce' to get the disk out of the VG?

What does 'vgdisplay -v vg00' show now? What about 'lvdisplay -v /dev/vg00/lvol?' for some of the vg00 lvol's?

If the disk is still showing up in the LV's then that may be the problem.

Re: Poor perfromance after breaking and removing mirror root disk???

I lvreduced the mirrors and physically removed the disks but did not remove it from LVM, in other words vgdisplay & lvmtab still shows it... but its only the root drive that slow access to the DB's that resides on vg01 are running fine

Patrick Wallek
Honored Contributor

Re: Poor perfromance after breaking and removing mirror root disk???

Try reducing it out of the VG.

# vgreduce -f vg00

Will force a reduce of missing PV's out of the VG.
Hein van den Heuvel
Honored Contributor

Re: Poor perfromance after breaking and removing mirror root disk???

Yes, those avserv time are horrible, but what is the access rate?

Is the system experiencing any actual performance issues, or are you just concerned about an ugly number on a report?

Could it be that from an HPUX perspective the system is 100% busy waiting for long times for responses which never come as the drive is gonzo?

Also, given a high read activity on VG00, some slowdown should be expected when removing a mirror member. From the "HP-UX Performance Cookbook":
"Sometimes for read-intensive workloads, mirroring can improve performance because reads can be satisfied from the fastest disk in the mirror"
Ergo: un-mirroring can decrease performance.

hth,
Hein van den Heuvel
HvdH Performance Consulting

Re: Poor perfromance after breaking and removing mirror root disk???

I just realized that there was a small lvol on the failed disk, that was NOT mirrored. I'm thinkning this may be partly causing the poor performance... but when I attempt to lvreduce it it fails, it basically says it cant access the drive. I think I will replace the drive and hopefully the vgcfgrestore will allow me to lvreduce it or mount it. We'll see :-)