[linuxperf] Some info to start with

[John Justice <justice@quantumres.com>]

A few writers have spoken up with a desire to edit.  Here's some jive on
filesystem tuning that I don't really have time to edit and commit to CVS.
Also, more information on this topic (I know someone said they liked
research) would be very useful.  An md and/or RAID overview couldn't hurt
either.

----------------------Begin article---------------------
When tuning hard drives for optimal performance, it can be helpful to use
several drives in a software RAID (redundant array of inexpensive disks).
The tool to use for this is "md".  md's documentation can get you through
the ins and outs of creating md RAID partitions, but it doesn't offer much
help when tuning for performance.  Here's an example and a rule of thumb to
help you out:

  Build the stripe set with your chosen chunk size:
    mdcreate -c64k raid0 /dev/md2 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
  Here, I'm using 64K chunks across 4 disks.  Start the device as usual
  (mdadd /dev/md2; mdrun /dev/md2)

  Next, make an ext2 filesystem with the "stride" parameter:
    mke2fs -b 4096 -i 16384 -R stride=64 /dev/md2
  Here, I use 4k blocks, 16k inodes, and the optimal stride is given by:

               chunk size 
   stride  =   ----------   *  (# of disks)  = 16 * 4 = 64
               block size

With this configuration, I was able to coax four 7200 rpm drives into
putting out 65MB/sec in filesystem throughput (measured with the Bonnie
benchmark).

------------------------End article-------------------------
***********************************************************
* John Justice              ** justice@quantumres.com     *
* Quantum Research Services ** http://www.quantumres.com  *
* Voice (919)544-4952       ** Fax: (919) 544-2918        *
***********************************************************

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