[Linux-cluster] RAW Devices performance issue

Shariq Siddiqui shariq.siddiqui at yahoo.com
Wed Feb 16 10:04:00 UTC 2011

Dear All,

I am going to install Oracle RAC on two Servers, With shared SAN storage 
(Servers and Storage is IBM)
OS = RHEL 5u5 x64 bit

And we used multipathing mechanism and created multipathing devices.
i.e. /dev/mapper/mpath1.

Then I created raw device /dev/raw/raw1 of this /dev/mapper/mpath1 Block device 
as per pre-reqs for Oracle Cluster.

Every thing looks good, But we faced the performance issue as under...

when we run command :
#dd if=/dev/zero of=/dev/mapper/mpath1 bs=1024 count=1000
the writing rate is approx. 34 MB/s

But If we run command
#dd if=/dev/zero of=/dev/raw/raw1 bs=1024 count=1000
the writing rate is very slow like 253 KB/s

Please advice how to tune the performance.

Best Regards,

Shariq Siddiqui

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