Re: Oracle RAC with ENBD

hi again, 

> > There is a paper from someone, who did this with NBD: http://www.fi.muni.cz/~kripac/orac-nbd/
> 
> If it is possible with NBD then it is possible with ENBD>
ok - so i should give it a try :)

> But the word "shared" makes me wonder! You can't in principle share
> remote devices because every kernel involved would have a different
> cached image of the device. They'd all be unaware of changes made by
> the thers if they were to areas hey already had cached.
yep - but didn`t the paper mention to make those devices RAW ?
Didn`t RAW mean something like "non cached" ?

from the document:
--snipp--
>Now block devices should be configured and you should be able to access 
>remote data. Furthermore Oracle Real application clusters need raw access 
>to shared disk subsystem so mapping raw devices to block devices is needed. 
>This could by done with standard raw command. 

>Syntax: 
>	/usr/bin/raw /dev/raw/raw<n> /dev/nb<n>
>Example: 
>	/usr/bin/raw /dev/raw/raw1  /dev/nb1
>	/usr/bin/raw /dev/raw/raw2  /dev/nb2
	>        /usr/bin/raw /dev/raw/raw3  /dev/nb3
	>        /usr/bin/raw /dev/raw/raw4  /dev/nb4
	>        /usr/bin/raw /dev/raw/raw5  /dev/nb5
--snipp--

> The only soluton is to not cache anything, something that can be done
> by doing direct i/o on the server (the -y switch?).  But how do you turn
> off caching on the client kernels?  You can't. All you can do is access
> the device with direct i/o there too. So it's an application-dependent
> thing.
Do I really need to turn off caching on the server ?
Think of each data file exported by one ENBD server to TWO ENBD clients  - 
that data travels from disk back and forth to the clients through the same _ONE_ 
ENBD Server process. Wouldn`t that be consistent data ?

> But you CAN do it provided you promise to use direct i/o (OPEN_DIRECT)
> on the clients at the application level and use direct i/o on the server
> too (-y ?)
Yes - Oracle does that OPEN_DIRECT afaik.

> I don't know. You can tell me!
hopefully soon :)

> Send money care of the elves :).
:)

roland