[CentOS] Format details for a raid partition....

Nataraj incoming-centos at rjl.com
Fri Oct 1 20:15:07 UTC 2010

Tom Bishop wrote:
> So I have been playing with a RAID 10 f2 ( 2 disks far layout) 
> setup...thanks for all of the advice..Now I am playing with the format 
> and want to make sure I have it setup the best that I can, my raid was 
> built using the raid 10 option with 2 disks with the layout=far, chunk 
> size 512....now I read all of the docs I could find about format and 
> stride and stripe size and this is what i came up with...
> mkfs -t ext4 -E stride=128,stripe-width=32 /dev/md0
> Someone let meknow if this looks right, but since i only have two 
> disks to get my stride 512/4k=128 and then to get my stripe 2/2*128/4=32
I have this in my notes for ext2/ext3 filesystem under raid 5.  You will 
have to see how your layout differs from raid5 in terms of distribution 
of data across the disks.

#       the optimal stride is given by:
#                chunk size
#       stride = ----------  *  ( num disks )
#                block size

Here is a framework of a script to test performance of various chunk 
sizes (came off of some webpage a while ago).  Optimal chunk size will 
of course depend on your application and the size of your writes and files..
        EXT2BLOCKSIZE=4096      # or 1024 or ???
        for CHUNKSIZE in 4 8 16 32 64 128 256 512
                stride=$(( $CHUNKSIZE * 1024 / $EXT2BLOCKSIZE ))
                .. create new /etc/raidtab and run the test
                mke2fs -b $EXT2BLOCKSIZE -m 1 -Rstride=$stride /dev/mdxx
                mount /dev/mdxx
                # whatever test ..

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