IO tuning for AIX running oracle ASM

bahard
bahard used Ask the Experts™
on
Hello,

Changing pbuf values (like pv_min_pbuf) has an IO performance change on ASM disks?

Thanks.
Comment
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
Most Valuable Expert 2013
Top Expert 2013

Commented:
No, it hasn't.

pv_min_pbuf is for LVM controlled hdisks (i.e. accessed via logical volumes) and not for raw disks as used by ASM.

wmp
Top Expert 2015

Commented:
ASM uses LVM raw volumes
LVM parameters apply, but since pbufs are auto-tuned by system no care needed there.
More gold is hidden around AIO tunables.

Author

Commented:
Hello gheist&wmp,

I had known that pv_min_buf does not have a control over ASM disks until I attended a powercare session by IBM and in this training session, the IBM expert said that actually it does. But I have no documentation of it so I am really in doubt about that.

What do you mean by "LVM raw volumes"? When defining ASM disks, we only use disks major and minor number, which means that it is only hdisk-related and there should be no relation with LVM.

And also, this is the first time that I see auto-tune parameters for IBM. If so, could you please explain why I see a regular increase in "blocked_io_count" in "lvmo -a" output. Is there a way to eable auto?

Kind Regards.
Become a Certified Penetration Testing Engineer

This CPTE Certified Penetration Testing Engineer course covers everything you need to know about becoming a Certified Penetration Testing Engineer. Career Path: Professional roles include Ethical Hackers, Security Consultants, System Administrators, and Chief Security Officers.

Top Expert 2015

Commented:
I do not know why oe would use PVs, as LVM adds ability to migrate data away from broken hardware while app keeps working....
Most Valuable Expert 2013
Top Expert 2013
Commented:
LVM raw volumes are logical volumes under control of LVM not bearing a filesystem but application-specific data.

LV have major/minor numbers just as hdisks do.

See all your LVs with

lsvg | lsvg -i -l

See your ASM volumes with

asmcmd volinfo -a

This is what "ioo -h" says to pv_min_pbuf:
... Useful to increase if there is a substantial number of simultaneous I/Os and if the number of "pending disk I/Os blocked with no pbuf" in vmstat -v is non-zero, which indicates that LVM had to wait for pbufs.
AIX does much auto-tuning, but you generally can't enable or disable it.
Top Expert 2015

Commented:
oracle uses AIO to queue requests to storage. if AIO queue is smaller than all pbufs, then obviously they go underutilized... (which is usually the case)

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial