[NTLUG:Discuss] RE: true hardware/intelligent ATA RAID -- Mylex->LSI, Intel I/O processors (3030x v. 3032x)

[Bryan J. Smith]

On Wed, 2004-07-21 at 12:25, Bryan J. Smith wrote:
> uc+DRAM:  $1,000+
> - StrongARM/xScale microcontroller based (e.g., Mylex eXtremeRAId)
>  ...
> You need something like a StrongARM or Xscale processor to deal with today's
> ATA/SCSI DTR rates, especially for RAID-0, 1, 0+1 reads/writes, or RAID-5
> reads.  Intel didn't buy Digital's fabs (and later Digital itself) for the
> Alpha, it bought it for rights to the StrongARM chip.  The Xscale is based
> on the StrongARM.
> IBM's Mylex division supports Linux very well as well.  Even the most entry-
> level StrongARM can push 5x as much data around as the fastest 100MHz i960
> design -- of which, Adaptec only uses a 66MHz and some of the early
> Promise SuperTraks used only a measly 33MHz.  The latter capped out at
> 40MBps, clearly because the slow i960 was a bottleneck!

Ack!  Shows how long since I've built a system with a Mylex card (2
years)!  If you go to Mylex.COM, it goes to LSI's Legacy RAID page.

Okay, did a bit of reseach:  
http://developer.intel.com/design/iio/index.htm?iid=ipp_embed+proc_iop  

As I mentioned earlier, the 8030x is i960-based.  You're talking a
single integer pipe microcontroller.  Pretty old, pretty crappy for
high-speed disk I/O.  Even by Intel's own marketing, you can only expect
a 25% performance increase with the "last generation" 80303.

The most you could hope for was 40-80MBps in a disk controller with the
i960 upto 100MHz.  You'll also note they are typically in 32-bit x 33MHz
PCI form-factors, although a few offer 64-bit, but the i960 wasn't
designed for it.  The 80303 survies because it is largely a "drop
in-replacement" for engineers for previous i960 designs, so they can
offer a 64-bit, 66MHz chip.  But you're not going to get much "real"
performance beyond 100MBps with it and tons of latency (even the
internal DTR is only 533MBps).

The newer XScale series of products are pretty modular.  They will all
be marked 8031x or higher.  The latest support PCI-X 1.0 bus arbitration
upto 64-bit x 133MHz, including on-board communication I/O (e.g., GbE). 
The XScale has upto 7-issue integer pipeline design, 32-bit ARM ISA with
64-bit data bus -- blows away traditional microprocessor design at I/O. 
You can push around GBps with these suckers, which means easily 3-5x the
"real" I/O performance in the 0.2-0.5GBps range.

Most controllers are designed for i960 because it is established and
well-known.  While that was great when disks were churning out less than
20MBps of DTR, we're now approaching 80MBps of DTR _per_disk_!  Not good
for today's disk performance.

So unless you really want a bottleneck, I _highly_recommend_ you
consider going StrongARM/XScale for a traditional microcontroller-based
RAID card.  Unfortunately, all LSI ATA RAID cards are only i80302 or
i960.  In fact, the only MegaRAID products with XScale are the ones with
"X" at the end.

Product Brochure:  
http://www.lsilogic.com/files/docs/marketing_docs/storage_stand_prod/rsabrochure.pdf  
If you can't afford that, 3Ware offers "real" 0.25GBps performance for
far less.


-- 
     Linux Enthusiasts call me anti-Linux.
   Windows Enthusisats call me anti-Microsoft.
 They both must be correct because I have over a
decade of experience with both in mission critical
environments, resulting in a bigotry dedicated to
 mitigating risk and focusing on technologies ...
           not products or vendors
--------------------------------------------------
Bryan J. Smith, E.I.            b.j.smith at ieee.org