I can not explain the poor perform of simultaneous access but
FYI you can't get 1.5Gb/sec from a sata interface - thats the
bit rate on the serial lines for commands and data not
the overall througput, expect no better than 70MB/sec on a
32/66Mhz PCI bus with todays SATA devices for sustained buffered data. 
Whats more most of the current SATA disks are PATA disks with a front
end chip so you end up with worse than PATA - but there
again nobody is claiming SATA is faster or better :-). I don't
have the 3112 (I have a CN2507) but I bet it isn't allowing overlapped 
access dispite the claim for "two 256 byte, per channel fifo's".
Either that or the PCI bus is bottlenecking

sebastien_erard@hotmail.com wrote:
> Hi,
> 
> I have a SATALink 3112 controller with two 120GB SATA hard drives.
> (see below the dmesg output for these devices)
> 
> If I access only one of them, I get up to 22MB/s trasfert rate on
> the first GB (ussing dd bs=256k count=4096). Using dd one both
> drives at the same time does not change much.
> 
> With a single partition one both of them, using bonnie++ (from
> pkgsrc-current) shows some tranfert rates up to 50MB/s with a 1GB
> file! (I checked this value with 'systat vm', it's impressive!)
> But with bonnie++ on both drives at the same time, I nearly got
> only 1MB/s (still systat vm).
> 
> My first idea was to use these two disks in RAID-0 (stripping).
> But I noticed this strange behaviour: poor performance when
> accessing both disks at the same time. Unusable with raidframe.
> 
> Is this a known limitation of the SiI3112?
> 
> Thanks for any answer,
> Sebastien
> 
> PS: It seems that dd is doing some very small transfers, even
>    when specifying bs=256k, something like 11k tps. With
>    bonnie++, I only see 700 to 800 tps. All of this observed
>    witt systat vm.
> 
> [dmesg for satalink0, wd0 and wd1]
> satalink0 at pci3 dev 12 function 0
> satalink0: Silicon Image SATALink 3112 (rev. 0x01)
> satalink0: SATALink BA5 register space disabled
> satalink0: bus-master DMA support present
> satalink0: primary channel wired to native-PCI mode
> satalink0: using ioapic0 pin 20 (irq 3) for native-PCI interrupt
> atabus2 at satalink0 channel 0
> satalink0: secondary channel wired to native-PCI mode
> atabus3 at satalink0 channel 1
> ...
> satalink0: port 0: device present, speed: 1.5Gb/s
> satalink0: port 1: device present, speed: 1.5Gb/s
> wd0 at atabus2 drive 0: <Maxtor 6Y120M0>
> wd0: drive supports 16-sector PIO transfers, LBA addressing
> wd0: 114 GB, 238216 cyl, 16 head, 63 sec, 512 bytes/sect x 240121728 
> sectors
> wd0: 32-bit data port
> wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
> wd0(satalink0:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) 
> (using DMA data transfers)
> wd1 at atabus3 drive 0: <Maxtor 6Y120M0>
> wd1: drive supports 16-sector PIO transfers, LBA addressing
> wd1: 114 GB, 238216 cyl, 16 head, 63 sec, 512 bytes/sect x 240121728 
> sectors
> wd1: 32-bit data port
> wd1: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
> wd1(satalink0:1:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) 
> (using DMA data transfers)
> ...
> 
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