Re: Question on ASM LUN size and adding datafiles

  • From: Taral Desai <taral.desai@xxxxxxxxx>
  • To: ksmadduri@xxxxxxxxx
  • Date: Sat, 20 Nov 2010 12:25:30 -0600

The way it distribute data you might end up with error saying that there is
no space on other disk to replicate data. I can't remember exact error.
Other issue would be combination of different disksize like lets say 10gb (3
disk group) you added 20 GB 4 th disk. in that you will not able to use more
then 10g. That relate to same as first issue.

Test Your self. Oracle need to format block before it has to write to it so
if it's done prior or latter i think doesn't make much difference in work
wise. Only thing is while you are running your load process if it's taking
to much resources then formatting make take bit time due to other latencies
but that can be a not a major difference performance wise.

I may be wrong so test it and see what happens.

On Sat, Nov 20, 2010 at 10:19 AM, Kumar Madduri <ksmadduri@xxxxxxxxx> wrote:

> Hello All:
> ASM LUN Size question:
> ----------------------------------
> Are there any disadvantages (in terms of imbalance and consequent
> performance impact) if you add different LUN sizes to the same disk group?
> Storage administrator usually gives us 90GB LUN Sizes ; But if they decide
> to give 60 GB LUN sizes and from a storage point of view, they  dont see a
> difference in giving us a 90 GB vs 60 GB LUN.
> My understanding is that , once ASM rebalance is complete, there would not
> be any performance issue or imbalance issue. Also,  since LUNS are logical
> units, I can still have different LUN sizes in the same diskgroup and would
> be ok. Ideally it would be good to get the LUNS of same size. I did read a
> few blogs where there were issues with different LUN  Sizes but that was
> more due to rebalance not happening to start with.
> Can you correct my understanding  if it is incorrect ?
> Adding datafiles
> ----------------------
> This is not related to the above clarification.  If I am doing a major
> application upgrade and I know couple of tablespaces are used extensively in
> the upgrade (I would be adding additional 200 GB of data as a result of
> upgrade in to these two tablespaces), my understanding is that since I know
> that this upgrade is going to take 200 GB of data, I would be better off in
> creating datafiles for those tablespaces and allocate the space in one go
> before the upgrade (like alter tablespace ttt  add datafile 'xxxxx' size 8g
> ) instead of alter tablespace tttt add datafile 'xxxxx   size 32m autoextend
> on next 32m maxsize 8192m  and let Oracle allocate extents as it needs (even
> though this is LMT, allocating extents in this manner may be less efficient
> than in one go especially when we know the volume of data to be loaded). Can
> you please clarify?
> Thank you
> Kumar

Thanks & Regards,
Taral Desai

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