Question about DMA speed of eSATA 600 drives.

[Roberto Ragusa]

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.

-- 
   Roberto Ragusa    mail at robertoragusa.it