On Wed, Feb 16, 2011 at 5:04 PM, Shariq Siddiqui <shariq.siddiqui@xxxxxxxxx> wrote: > > > 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. Shouldn't you ask Oracle about that? My GUESS is that in the first one the I/O is buffered, while in the second /dev/raw/raw* is simply a block device opened with O_DIRECT (thus bypassing buffer cache). You may want to retry dd with "oflags=direct" and compare the results. You might want to look at http://en.wikipedia.org/wiki/Raw_device http://download.oracle.com/docs/cd/B19306_01/relnotes.102/b15659/toc.htm#CJAICHEG Again, better ask Oracle if you want to be sure. -- Fajar -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
