Post by Tony Hall
I've bought some more storage for my photo backups, which will mean
moving many terabytes of data around.
Is there a better, more reliable method that would be preferable to
simply using drag 'n' drop in the Finder, maybe something that performs
robust error checking etc. (*Not* command line - my brain doesn't work
I already have SuperDuper! and ChronoSync - would these offer any
advantages over the Finder?
Any software recommendations? (Preferably low cost as I only do this
once every few years.)
Many thanks for your thoughts and advice.
OK Some thoughts ....
Do you have master files for your photos and - separately - backup
copies? I suspect from the way you've worded the question that you
don't, so I'm not sure exactly what it is you are trying to achieve.
Computers generally distinguish between "move" and "copy". They may
make assumptions - thus on a Windows PC "move" happens by default when
the source and destination folders are on the same logical device
(generally). When source and destination are on different physical
devices the default operation is "copy". Macs may be different in this
Further, if there are restrictive ownership settings on the files in the
source folder these might or might not be transferred to the files in
the destination folder, particularly if the destination folder is
"owned" by another user. Moving files about between user folders on a
Windows server is a classic cause of such problems because ownership
does not change. I think Novell Netware made the opposite assumption
and changed ownership permissions to match that of the destination
folder. But whatever happens, for some users and some requirements the
default option will be incorrect.
The problem with "move" when it is applied to many files may be that
each source file is first copied then the source is deleted before
working on the next file. Thus files may be lost if the copy process
has failed. Typically on Windows, if one such failure occurs then the
whole "move" terminates - leaving some files on the source and some on
the destination. This may also happen on a Mac.
In addition, the mouse-driven "drag-n-drop" move is very susceptible to
human error. I've seen users think they have deleted many files when
they have inadvertently dropped them inside the wrong folder. An
explicit "copy" can sometimes be undone if the user makes that sort of
This is where your requirement for robustness is relevant.
Probably the safest procedure is never to "move" anything. If you
always copy from source to destination then nothing is at risk of
unexpected deletion. Then ideally you should log every file copied -
but reading through that log to spot the odd failure in perhaps
thousands of lines is a real challenge.
This is where command line tools really do come into their own, and are
well worth learning. For example, a command could:
A. Specify a copy from source to destination, but only log the files
that would be copied.
B. Carry out that copy, creating a new log file.
... then you could compare the log files to verify they match - giving
you confirmation that the procedure has worked.
C. Compare each source file in turn with the destination file - again
logging the result. This gives more confidence that the procedure has
D. Repeat the process with the destination directory on a different
device - you then have a trustworthy duplicate copy.
Windows has "Robocopy" which together with command line scripts can
achieve such things. Given that Linux underlies the Mac operating
systems I'm sure an exactly similar scripting process would achieve what
you want - it must have the necessary tools.
Finally - if you really do have master files and backups - never change
a master version without having a trustworthy backup.
So if what you want to achieve ultimately is to move all the master
files to new physical storage - try this:
Create the new storage structure on the new hardware, and restore the
files from the backup to that new hardware in the organisation you now
require; then create a separate new backup which replicates the new
organisation. Finally delete the files from their original storage
location, and allow the original backup to be re-used.
You can execute each step and test it for correctness before moving to
Hope this helps.