Re: [tlug] USB3 hard disks

[Kalin KOZHUHAROV <me.kalin@example.com>]

On Sun, Jun 1, 2014 at 4:00 PM, Travis Cardwell
<travis.cardwell@example.com> wrote:
> On 2014年06月01日 14:15, Darren Cook wrote:
>> Quick question: I've two USB3 sockets. If I plug two hard disks in, and
>> want to copy the entire contents of one drive to the other drive,
>> roughly how long will it take? Does anyone do something like this as
>> part of their backup strategy? (No longer having RAID-1 on either my
>> main notebook, or my backup device(s), is making me nervous.)
>
Those "two USB3 sockets" might actually be on the same bus (=hub),
which will limit your I/O even further.
I tend to avoid any USB3 HDDs unless forced to and I use cases where
bare drives are slid into. For external storage I use eSATA - it is
faster.

> By "copy the entire contents," do you mean copying the whole drive using a
> command like `dd`?  If so, here are a few ways to get an estimate of how
> long it will take:
>
> A fancy option is to monitor the progress of the copy using `pv` (which
> Kalin recommended in his presentation), which will even show you a countdown:
>
>     $ dd if=/dev/SRC | pv | dd of=/dev/DST
>
# pv -petrab /dev/SRC >/dev/DST

iff they are the same number of blocks, but I'd strongly recommend against that.
You can calculate your readspeed like:
$ pv -petrab /dev/SRC >/dev/null
(and Ctrl+C after few GB)

> That is probably not an option in your case, unless you can take the hard
> drives out of the USB interface cases.
>
This is what I recommend, esp. if they are good SATA drives (7200RPM).
You can usually get 100MB/s. USB3.0 usually gives 40-60MB/s .

1TB @50MB/s (=180GB/h) needs about 6 hours. Make sure they are cooled
well during the time.

Kalin.