Question about DMA speed of eSATA 600 drives.

[jd1008]

On 09/23/2014 11:20 AM, Roberto Ragusa wrote:
> On 09/23/2014 03:28 AM, jd1008 wrote:
>> Have an external drive, wd20npvx , 2 tb.
>> It spinsx at 7200rpms, and is touted to have 600 gigabit/s
>> on the wire speed. However, fc20 always connects it as
>> having dma100, when the esata port supports 300 gigabits/s
>>
>> So, what's with Fedora to limit it to dma100?
>>
>> To wit:
>> [ 3571.062358] ata11: SATA link up 3.0 Gbps (SStatus 123 SControl 0)
>> .
>> .
>> .
>> [ 3571.063587] ata11.00: ATA-9: WDC WD20NPVX-00EA4T0, 01.01A01, max UDMA/133
>> .
>> .
>> [ 3571.065292] ata11.00: configured for UDMA/100
> You are confusing numbers. Forget about 600gigabits/s.
>
> SATA is 1.5Gpbs or 3.0Gbps or 6.0Gbps.
> Your drive link is working at 3.0Gbps, probably because you do not
> have a 6.0Gbps controller.
> (bps is bit per seconds, you have to divide by 10 to obtain bytes
> per second, 150MB/s, 300MB/s, 600MB/s)
>
> PATA had a lot of different transfer mode, the best of them were
> the UDMA/100 (100MBps) or, more rarely, UDMA/133 (133MBps).
> (Bps is bytes per second, 100MB/s, 133MB/s)
>
> AFAIK, UDMA values are often printed in SATA logs, with no real
> meaning at all.
>
I do know that if the sata controller operates at 3g bits/s, then the 
on-the-wire
speeds of transfer to/from computer/disk will be 3g bits/s.
If the UDMA values in the log
So, how can I ascertain if I am getting much better transfer (read/write)
speeds without doing io from one unmounted partition of drive A to an 
unmounted
partition on disk B?
Usually I use dd with bs=512M or 256M (in case I have a lot of programs 
running).
I have seen 65 mbytes/s, but that is achievable even with UDMA133 PATA 
drives spinning
at 7200rpm.