[linux-lvm] I:LVM Raw Oracle 9i RAC

[Bernat Covacho, Jose Maria]

Hello, we have a RedHat Avanced Server 2.1 with kernel version 2.4.9-e.12smp and we use lvm version 1.0.3 (yes I know that the latest "one" version is 1.0.7). I think that the version 2 is too much advanced for us. 
 
We have a very strange problem with lvm, oracle and raw devices. If we take a logical volume manager and test it with a simple dd we get:
 
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time dd if=/dev/MKTP/strip32 of=/dev/null bs=512k count=2048 
2048+0 registros leídos
2048+0 registros escritos
 
real    0m13.394s
user    0m0.000s
sys     0m6.090s
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 
Ok, It works fine, we have 1Gbyte in 13 seconds.
 
Now we bind this logical volume to a raw device
 
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raw /dev/MKTP/strip32 /dev/raw/raw15
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 
and we try with this:
 
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time dd if=/dev/raw/raw15  of=/dev/null bs=512k count=2048 
2048+0 registros leídos
2048+0 registros escritos
 
real    0m14.828s
user    0m0.020s
sys     0m6.180s
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 
The same time, more or less, all it's ok. 
 
Now we want use this raw (raw15) with oracle. We create a oracle tablespace put data into. We can access it through oracle.
 
We stop oracle. Now we repeat the same dd:
 
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time dd if=/dev/raw/raw15 of=/dev/null bs=512k count=2048
2048+0 registros leídos
2048+0 registros escritos
 
real    0m48.971s
user    0m0.010s
sys     0m11.590s
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 
Now we have 48 seconds, why?, The only one difference is the tablespace creation.
 
We try the same process without lvm and we have the same good time in three cases.
 
There are some problem with lvm, raw and oracle?
How can I avoid this?
 
Thanks in advanced
 
 
 
 
 
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