Re: Striping on striping - good, bad, indifferent?

Hello, Roger.

This is called vertical and horizontal striping. Horizontal striping is
the stripe across the physical disks, creating a RAID
Array/Group/Rank/whatever on which a LUN is created. Vertical striping
is striping across LUNS on different RAID groups. It's usually
implemented on the backend in your SAN, but I don't see any reason off
the top of my head why it can't work with OS-level vertical striping.
It can be very helpful if you're pushing large I/O's in pretty much any
HPC environment.

The super-critical thing to be aware of is that you must not vertical
stripe across LUNs on the same horizontal stripe/RAID group. This will
cause head thrashing.

Be sure to test your I/O throughput both ways and let us know what you
find out. :-)

Alex Paschal
Unix Administrator
Freightliner, LLC
f y cn rd ths y mst b sng nx


-----Original Message-----
From: IBM AIX Discussion List [mailto:aix-l@xxxxxxxxxxxxx] On Behalf Of
Roger Deschner
Sent: Tuesday, May 22, 2007 4:05 PM
To: aix-l@xxxxxxxxxxxxx
Subject: Striping on striping - good, bad, indifferent?

I'm setting up a Logical Volume which will consist of two identical
hdisks. Each hdisk will actually be a hardware RAID10 array. (SSA in
this case, though the underlying hardware technology shouldn't matter.)

Within AIX JFS2, should I stripe between those two hdisks, or not? The
application will be /var/spool/mail, so very few of the reads or writes
will exceed the PP size of the VG. Are there any peculiar issues here to
be aware of, such as the relationship of the hardware (SSA) stripe size
to the AIX JFS2 stripe size?

What I am hoping for is to get the benefits of striping across all the
physical disks in both of the arrays, thereby overcoming the 8-way
stripe limit in SSA.

Roger Deschner University of Illinois at Chicago rogerd@xxxxxxx
==== "Research is what I'm doing when I don't know what I'm doing." ====
========================= -- Wernher von Braun =========================

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