Re: SATA vs PATA
On Mon, Aug 27, 2007 at 11:13:33AM -0700, cls@truffula.sj.ca.us wrote:
> The instantaneous peak throughput of the original
> (four bytes wide, 33 MHz) PCI bus is 132 MB/sec. In real life
> you're not going to see over 90. So a SATA-II controller
> on a regular PCI card is bottlenecked at the motherboard slot.
> (So is 1000BASE-T Ethernet.) That's one reason "real hardware"
> RAID works better than "fakeraid."
> The smallest PCI Express (PCI-E) configuration should do 250 MB/sec
> in each direction simultaneously. A motherboard with PCI-E
> designed for workstations may bottleneck at the southbridge.
>
> You'll have to do some research to find a configuration that
> can run two SATA-II drives simultaneously at their full data rate.
> You'll also have to check around to see if the Linux driver knows
> how to run any particular controller in SATA-II mode.
> And there are still lots of workstation type motherboards that only
> do SATA-I.
My Asus M2N-SLI Deluxe AM2 MB with Athlon64 3800+ CPU has 6 SATA-II
ports with the nVidia chipset and one internal and one external eSATA
with an addition chip (JMicron?) on the MB as well. Here's some lines
from my dmesg:
ata1: SATA max UDMA/133 cmd 0x9F0 ctl 0xBF2 bmdma 0xE000 irq 58
ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
ata3: SATA max UDMA/133 cmd 0x9E0 ctl 0xBE2 bmdma 0xCC00 irq 66
ata3: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
ahci 0000:06:00.0: AHCI 0001.0000 32 slots 2 ports 3 Gbps 0x3 impl SATA mode
ata7: SATA max UDMA/133 cmd 0xFFFFC20000040100 ctl 0x0 bmdma 0x0 irq 74
ata8: SATA max UDMA/133 cmd 0xFFFFC20000040180 ctl 0x0 bmdma 0x0 irq 74
I don't have hdparm installed and I don't have any real way of testing
the throughput easily right now. Len Sorensen on debian-amd64 yesterday
went through the math on SATA speed, PCI-e speed, CPU bus speed, etc.
Check the archives and review that.
The upshot was that a hardware raid card makes sense if you're going to
do raid5 and you get a card good enought that it can beat the CPU at the
game. Likely, this means a PCI-e x8 card (3Com was mentioned) that you
can attach to the spare x16 slot (intended for the second video card in
an SLI setup).
Other than this case, it probably doesn't warrant a raid card; if you
really need that kind of I/O throughput you're probably looking at
server hardware that uses SAS instead of SATA. Although, according to
wikipedia, a SAS enclosure can use SATA drives in some kind of
compatibility mode.
In any event, if you're choosing between PATA and SATA, go with SATA
unless:
1. performance isn't an issue
2. you can get a huge deal on a good PATA drive.
Doug.
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