On Fri, Sep 07, 2018 at 11:10:08AM +1000, Cameron Simpson wrote:
> On 06Sep2018 19:20, Ranjan Maitra <maitra@email.com> wrote:
> >I have two drives mounted on a F28 system. Both are identical 4TB
> >drives. The second one is empty. I am concerned about the first
> >one failing so would like to copy the contents (which are around
> >3.7 TB) to the second.
> >
> >What is the fastest way to copy the contents of the first drive to
> >the second? I was using rsync, but is there a better way?

while the other suggestions might be faster, I prefer to use dd
(or ddrescue) 'cause it gives a bit-for-bit copy of everything
on the drive, partitions and all. ddrescue is handy in case it
finds spots that are hard to read on the source drive, it goes
back and retries them til it gets a good read.


>
> I like "cp -a", it is faster than rsync. Rsync's strength is
> incremental update: make a sweep afterwards with rsync to convince
> yourself it is correct.
>
> Even faster is a tar pipeline:
>
>  cd /drive1
>  tar cf - . | ( cd /drive2; tar xf - )
>
> because both cp and rsync do one file at a time. There will
> inherently be small pauses at each file boundary. Actually, rsync
> might stream a little.
>
> Using piped tars and many files, particularly many small files, the
> first tar can get ahead of the second tar for better throughput -
> the data queued in the pipe (which has a buffer, and a generous one
> on Linux) allows the first tar to proceed until the pipe is full if
> the second tar is blocked.  (The second tar will of course be
> blocked writing to drive2, but it won't be blocked reading from
> drive1 because the first tar can read followon files from drive1
> which the second tar reads from the pipe).
>
> However, if you're already a significant way through your copy you
> may as well stick with rsync unless you can easily do things in
> chunks, as changing systems means wasting time copying already
> copied data. Do a "df" and make an estimate.
>
> If there are still hours to go you could consider switching methods
> and doing the uncopied subdirectories:
>
>  cd /drive1
>  tar cf - uncopieddir1 uncopieddir2 ... | ( cd /drive2 ; tar xf - )
>
> and then come back with rsync afterwards to clean up the rest:
>
>  rsync -iaP /drive1/ /drive2/
>
> Cheers,
> Cameron Simpson <cs@cskk.id.au>
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