[CentOS] Best mkfs.ext2 performance options on RAID5 in CentOS 4.2

[Bryan J. Smith]

Aleksandar Milivojevic <alex at milivojevic.org> wrote:
> What I found with an old(er) 3ware 7500-8 (does not use
> same device driver as 9xxx cards) in RAID5 configuration
> was that it makes big difference using ext2 or ext3
> (doubles the write speed, no effect on read speed).

Of course.

3Ware pairs its 64-bit ASIC in the 7000+ series with 1-4MiB
of 0 wait state SRAM (Static RAM).  That gives you the utmost
in non-blocking JBOD, RAID-0, 1 and 10 performance.  That's
won't cache much more than a few (standard) 32KiB blocks --
definitely not ideal for any multi-staged writes (such as
journaling).

The 9500S adds 128+MiB of multi-wait state SDRAM (Synchronous
DRAM) which can buffer a lot more.

The 9550SX actually now splits the design into the legacy,
non-blocking ASIC+SRAM plus a new embedded PowerPC 400 series
with its own 128+MiB of DDR2 SDRAM for the ultimate in a
buffering controller card.  When RAID-5 is used, or extensive
buffering is needed, the 64-bit ASIC (which is also the bus
arbitrator) switches the incoming stream into the SDRAM which
is then serviced by the embedded PowerPC 400 series.

> With ext3 I used internal journal (external migh have
> helped, but haven't tested it).  Changing journaling 
> options and/or journal size had almost no effect.  Anyhow,
> journaling (using default options, internal journal) should
> not have that high impact on write speed (not even close).

Again, considering the fact that the 7000/8000 series have an
extremely small -- only 1-4MiB -- "0 wait state cache"
instead of a much larger amount of "multi-wait state SDRAM
buffer," this is not unexplained.  3Ware 7000/8000 series
want to stream sequential writes -- especially when it comes
to RAID-5.  If not, it stalls.

> The card was considerably faster with 2.4 kernel than with
> 2.6 kernel (tests run on same hardware, same configuration,
> ext3 file system).  About 20% faster writes and 40% faster
> reads.

Hit 3Ware's site on optimizing the kernel 2.6 settings for
the card.

And be sure to get the latest firmware for the 9500S -- that
makes all the difference!

The 7000/8000 series firmware has been mature for years at
7.7.1 last time I checked.

If the new 9550SX is any suggestion, the 64-bit ASIC design
is just not going to cut it at RAID-5 writes versus a full
microcontroller.

AS a result, I can't recommend the 9500S.
The verdict is still out on the 9550SX.
But there is much promise thanx to AMCC.
They _know_ the embedded PowerPC 400 series in and out.

Tom's Hardware Review just did a recent I/O queuing
comparison, not actually benchmarks or CPU-interconnect load
comparisons.  It was rather limited in anything, although the
embedded PowerPC-based 9550SX challenged the new X-Scale
based Aerca's to keep up (and the X-Scale based LSI 300-8X
wasn't exactly as good).


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