On Thu, 2004-09-16 at 23:37, Patrick Grantham wrote:
> I used an adaptec 2910 sata RAID card with 65mb cache and four ports.
Did you mean the Adaptec 2410?
The 2400/2800 series use an Intel i960 series microcontroller and ECC
DRAM. They are based on the original DPT design, inherited by Adaptec,
and are I2O-compliant -- hence they use the dpt_i2o driver.
The 4-channel SerialATA 2410 specifically uses the i80302 with 64MB of
fixed PC100 ECC SDRAM, while the 8-channel SerialATA 2810 uses the
i80303.
I'm not a huge fan of the 32-bit i960 microcontroller. It was fine when
Ultra40 SCSI was the heyday, but it's too slow for today's block
transfer speeds. Intel has proliferated its Digital StrongARM-based
XScale as its successor for the past 5 years. You'll find it in
high-end SCSI RAID controllers.
The i960 w/DRAM is fine for buffering RAID-5 writes. And the
80302/80303 @ 66MHz** with the 300 series I/O peripherals are good for a
60-90MBps sustained DTR. But, IMHO, it's far too blocking for ATA doing
RAID-0, 1 and 0+1 -- direct, non-blocking I/O is what makes ATA more
ideal than SCSI. Wait states in the microcontroller+DRAM approach
affect response time and throughput.
[ **NOTE: This is still better than most in the Promise SuperTrak (not
to be confused with the "cheap" FastTrak) series, which shipped with
measly 33MHz i960 controllers early on. They topped out at 40-50MBps in
most benchmarks -- not good. ]
The 3Ware Escalade 7000/8000 differ completely from all other
intelligent ATA or SCSI RAID designs. Instead of the
microcontroller+DRAM approach, they use custom 64-bit ASIC logic with 0
wait state SRAM (that's Static RAM, not SDRAM). SRAM is a true clocked
boolean logic (CBL) circuit, and not a simple DRAM cell that leaks and
has high latency times (typically 45ns+ -- even for SDRAM -- on
reads/operations). SRAM means reads are 0 wait state as well as writes
(synchronous DRAM mitigates the latency for writes, but not for
reads/operations, long story). This is how high-end network switch
fabrics work for Ethernet -- ASIC+SRAM (possibly in tandem with a
microcontroller+DRAM for more advanced layer-3 routing). The positive
of the ASIC+SRAM is that RAID-0, 1 and 0+1 writes are direct,
non-blocking -- most ideal for ATA's non-blocking access.
The downside to this approach is that SRAM is very large and expensive.
So you can only get about 2-4MB of SRAM in the same cost/space as
64-128MB of SDRAM. The result is that it doesn't buffer RAID-5 writes
as extensively, and the cache can overflow easily if you have lots of
random, RAID-5 writes. Even the high-end, 12-channel 3Ware 7506/8506-12
cards only have 4MB of SRAM.
The new 3Ware Escalade 9000 is the best of all worlds. It combines the
same 64-bit ASIC core, but with both SRAM and added PC133 ECC SDRAM
(128MB base, upgradable to 1GB, but 3Ware has only tested performance up
to 256MB). You'll pay an extra $50-100 for it over the 8000 series, but
it's worth it.
> It was not cheap,
Of course not. Instead of just a simplistic, 2-channel ATA controller,
you now have a full i960 microcontroller, 64MB of SDRAM and 4-channels
for ATA. It's basically a SCSI RAID card, only the SCSI host adapter
has been switched out for ATA channels.
> but it was a breeze to setup on red hat 9.
That's because of the dpt_i2o driver in the kernel. Thank DPT. Adaptec
has a pretty long history of only supporting retail, non-RAID, cards for
Linux. I know some of the guys at the Orlando support location.
> Not firewire, but does have an option to adapt the internal sata
> ports to external.
Most do.
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