Question about DMA speed of eSATA 600 drives.

[Roberto Ragusa]

On 09/23/2014 08:31 PM, jd1008 wrote:
> 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.

Try

hdparm -t /dev/sda    (if your drive is sda)

this will do a speed test reading the first part of the disk.

Consider that:

- the beginning of the disk is faster then the final part (which can be about
half speed)

- normal drives have actual physical speed from 50MB/s to 200MB/s, even if
the SATA link permits a faster speed

- your drive is a "WD Green", which are generally quite slow, do not expect
spectacular numbers

Finally, if you get significantly slower numbers for /dev/sda1 with respect
to /dev/sda, maybe your partitions are not well 4k aligned (this happens when
the partitioning tool is too old).

-- 
   Roberto Ragusa    mail at robertoragusa.it