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Oracle raw volume size

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Jakes Louw
Trusted Contributor

Oracle raw volume size

Hi all,

Since time immemorial, we've been using raw datafiles in our Oracle databases.
We usually create the LVOL with a size exactly 4MB larger than the storage statement that is used when the datafile is added to the tablespace, but for the life of us, we can't remember WHY!
We seem to think there is some "overhead" space needed by Oracle, and we don't know whether this somehow relates to the guaranteed free space that is normally kept by the OS in filesystems (free_space_percent)?

Can anybody shed any light, or are we slavishly following an old practice that no longer is required?
Trying is the first step to failure - Homer Simpson
5 REPLIES
Jean-Luc Oudart
Honored Contributor

Re: Oracle raw volume size

We don't use raw devices but Oracle requires the 1st block for itself.
cf. attachment from Metalink doc id 146384.1

Regards,
Jean-Luc
fiat lux
Jean-Luc Oudart
Honored Contributor
Solution

Re: Oracle raw volume size

sorry,
forgot to attach the doc
Regards
Jean-Luc
fiat lux
Jakes Louw
Trusted Contributor

Re: Oracle raw volume size

Thanks, Jean-Luc.

Seems like we've been wasting a lot of space over the years, for nothing.......
Trying is the first step to failure - Homer Simpson
Hein van den Heuvel
Honored Contributor

Re: Oracle raw volume size

> Thanks, Jean-Luc.
> Seems like we've been wasting a lot of
> space over the years, for nothing.......

Well Jakes, if you like so many create your datafiles as a 'round' number of megabytes like 512MB or 4096MB and your PE is 4MB then you didn't really waste anything because you'll need a whole PE more for being a byte over.
'course you could have created the LV first (as a nice round number because you have no choice! :-), and then back-tracked the Oracle filesize as LV-size minus overhead.

I also recall liking to round-up to full MBs, to help dd scripts. It allows you to copy with for example bs=1024k without errors but the details escape me for now.

Finally... 'a lot' is probably less than 1% anyway assuming the datafiles are a few 100 MB.


Cheers,
Hein.
Jakes Louw
Trusted Contributor

Re: Oracle raw volume size

Hein

You are correct: the PE size is of course the real issue. With VGs of over 750GB, we often have to modify the PE size to be 8MB (in order not to exceed the published limits for MAX PE per PV, etc).
So we sometimes waste 7MB per datafile. Our local Oracle "standards" usually mean that datafiles are 2GB (2000MB, not 2048!), so if we have a 300GB tabelspace, we would have (obviously) 150 datafiles, with a wastage of 7MB minimum per datafile. That's 1050MB wasted! Not a lot when thinking of a 300GB tabelspace, but I'm a real miser...;->
Trying is the first step to failure - Homer Simpson