Can I rely on "copy" command?

[Walter R.]

I often have occasion to copy or move large blocks of files from one
partition to another.

Win XP SP2 has never told me yet that it has lost a byte here or a byte
there. Can I assume that all transfers are done flawlessly and with zero
data loss? Will Windows let me know if it accidentally loses or mangles a
few bytes while transferring data?

 

[Bob I]

I often have occasion to copy or move large blocks of files from one
partition to another.

Win XP SP2 has never told me yet that it has lost a byte here or a byte
there. Can I assume that all transfers are done flawlessly and with zero
data loss? Will Windows let me know if it accidentally loses or mangles a
few bytes while transferring data?

How would it know? It doesn't do a bit by bit copy verify. On the other
hand, when the system doesn't suffer hardware failure it works great.
The majority of the "data loss" is user error, followed by outright
drive failure. (which the user didn't backup)

 

[smlunatick]

I often have occasion to copy or move large blocks of files from one
partition to another.

Win XP SP2  has never told me yet that it has lost a byte here or a byte
there. Can I assume that all transfers are done flawlessly and with zero
data loss? Will Windows let me know if it accidentally loses or mangles a
few bytes while transferring data?

Nothing is every fool-proof. Xcopy has been around for some time and
may be reliable.

 

[Walter R.]

Well, I was wondering if it uses some kind of checksum before and after the
transfer. It should. Otherwise, Windows would be inherently unreliable.

Anyone know?

 

[Pegasus \(MVP\)]

I often have occasion to copy or move large blocks of files from one
partition to another.

Win XP SP2 has never told me yet that it has lost a byte here or a byte
there. Can I assume that all transfers are done flawlessly and with zero
data loss? Will Windows let me know if it accidentally loses or mangles a
few bytes while transferring data?

Nothing is every fool-proof. Xcopy has been around for some time and
may be reliable.

==============

.. . . and it has a /v (verify) switch!

 

[Bob I]

Nothing is every fool-proof. Xcopy has been around for some time and
may be reliable.

==============

. . . and it has a /v (verify) switch!

Don't bet on that.

Using /v
Windows XP does not use this command. It is accepted only for
compatibility with MS-DOS files.

and

VERIFY ON, COPY /V, XCOPY /V Commands Do Not Compare Data
http://support.microsoft.com/kb/126457

 

[John McGaw]

Well, I was wondering if it uses some kind of checksum before and after the
transfer. It should. Otherwise, Windows would be inherently unreliable.

Anyone know?

Well, even if _XP_ doesn't do it, there is nothing to stop _you_ from
generating a checksum or hash before the copy and then it afterward to make
sure that it worked properly. You could do a simple CSV. Or do an MD5. Or
even generate 10% of PAR2 files and copy them along with the originals and
then your copies will be to a large extent self-repairing even if something
goes awry.

John McGaw
http://johnmcgaw.com

 

[Pegasus \(MVP\)]

Don't bet on that.

Using /v
Windows XP does not use this command. It is accepted only for
compatibility with MS-DOS files.

and

VERIFY ON, COPY /V, XCOPY /V Commands Do Not Compare Data
http://support.microsoft.com/kb/126457

Well, I learn something new every day! BTW, I assume you meant to write
Windows XP does not use this switch instead of
Windows XP does not use this command.
because the command "xcopy.exe" is fully supported under WinXP (even though
it is now deprecated in favour of robocopy).

 

[HeyBub]

Don't bet on that.

Using /v
Windows XP does not use this command. It is accepted only for
compatibility with MS-DOS files.

Whatever. It still has the "/V" switch, even if the switch is a no-op.

Then there's the placebo effect...

 

[Pegasus \(MVP\)]

Then there's the placebo effect...

ROFL!

 

[LVTravel]

I often have occasion to copy or move large blocks of files from one
partition to another.

Win XP SP2 has never told me yet that it has lost a byte here or a byte
there. Can I assume that all transfers are done flawlessly and with zero
data loss? Will Windows let me know if it accidentally loses or mangles a
few bytes while transferring data?

While what others have said is true, there is one other issue with Copy. If
you use copy to copy a group of files with a wildcard and anything goes
wrong with the copy, it is automatically terminated at that point and
further files are not copied.

Xcopy does have a switch to ignore errors but that isn't a good feature in
the respect that you need to ensure a complete copy. Robocopy is better in
this respect.

There is another free program xxcopy.exe that will do what you want also.
It has a /v2 switch which will verify on a byte for byte basis that robocopy
won't. If you are using XXCopy in a corporate environment, there is a Pro
version that you can test drive for 60 days.

This is a biased report on the differences between Robocopy and XXCopy
http://www.xxcopy.com/xxcopy30.htm

For XXcopy download see: http://www.xxcopy.com/index.htm#download and click
#4 then download the .zip file.

I am not affiliated with the company in any way other than as a free user of
the software.

 

[Patrick Keenan]

I often have occasion to copy or move large blocks of files from one
partition to another.

Win XP SP2 has never told me yet that it has lost a byte here or a byte
there. Can I assume that all transfers are done flawlessly and with zero
data loss? Will Windows let me know if it accidentally loses or mangles a
few bytes while transferring data?

Generally, the answer to this is "no". The copy command has a rather
annoying response to errors, which is to give up and exit. This leaves
you with no real idea of where or when the error occurred.

Better to use another copy utility that does not behave this way. Xcopy /v
is a good start, but I often use a program called FileSync that has a GUI,
keeps track of errors it encounters, and can do bit-by-bit comparisons of
large groups of files.

HTH
-pk

 

[Bob I]

Well, I learn something new every day! BTW, I assume you meant to write
Windows XP does not use this switch instead of
Windows XP does not use this command.
because the command "xcopy.exe" is fully supported under WinXP (even though
it is now deprecated in favour of robocopy).

I presume the "writer" of the Help file meant that, As I actually
copy/pasted directly from Windows Help and support. ;-) To see this
yourself, look up Xcopy in Help and Support, and click the Xcopy link,
scroll past the first "/v" that claims to compare file contents, and
look at first entry in the Remarks section. Also notice that the Exit
Error codes do not provide for any "file comparison error".

 

[John John (MVP)]

I presume the "writer" of the Help file meant that, As I actually
copy/pasted directly from Windows Help and support. ;-) To see this
yourself, look up Xcopy in Help and Support, and click the Xcopy link,
scroll past the first "/v" that claims to compare file contents, and
look at first entry in the Remarks section. Also notice that the Exit
Error codes do not provide for any "file comparison error".

Here on my antique still in use NT4 box it says:

/v
Verifies each file as it is written to the destination file to make sure
that the destination files are identical to the source files. This
switch is ignored because the functionality is inherent to the
Windows NT operating system. The switch is accepted only for
compatibility with previous versions of MS-DOS.

John

 

[Bob I]

Here on my antique still in use NT4 box it says:

/v
Verifies each file as it is written to the destination file to make sure
that the destination files are identical to the source files. This
switch is ignored because the functionality is inherent to the Windows
NT operating system. The switch is accepted only for compatibility with
previous versions of MS-DOS.

John

Yes, one has to "trust" that Windows did what you told it to do, or
"check it yourself". ;-)