How reliable is zipping in Windows 7 Explorer?

[AndyHancock]

There have been times in the past when a zip file I created was
corrupt (or became corrupt somehow). I encountered this either using
WinZip or command-line zip, possibly in old Unix environments. To me,
there is a risk in relying solely on zip archives and deleting the
original unzipped files. The risk isn't only in losing one file that
is corrupt -- any corruption anywhere in the entire archive could
render all the files therein inaccessible. Hence, the risk increases
with the size of the archive.

How reliable is the zip that is native to Windows 7? In addition to
that general question, what about specifically for files in the
Gigabyte range (fraction of a GB or several GBs)? If it is very
reliable, then I will use the Windows 7's "compressed (zipped) folder"
to create archives for writing to DVD.

I am using Windows 7 Professional 64-bit. I want to avoid discussion
about Windows 7 backup as it is not suitable for my specific purposes.

[Char Jackson]

On Sun, 6 Jan 2013 13:51:53 -0800 (PST), AndyHancock

Post by AndyHancock
There have been times in the past when a zip file I created was
corrupt (or became corrupt somehow). I encountered this either using
WinZip or command-line zip, possibly in old Unix environments. To me,
there is a risk in relying solely on zip archives and deleting the
original unzipped files. The risk isn't only in losing one file that
is corrupt -- any corruption anywhere in the entire archive could
render all the files therein inaccessible. Hence, the risk increases
with the size of the archive.

If you're concerned with the integrity of any data files, zip or otherwise,
one way to get peace of mind is to use Quickpar to create a recovery set.
Normally, 10% is a nice round number to use, but feel free to adjust the
settings as you see fit. With a Quickpar recovery set, not only can you know
for sure whether your data is intact, but if it's damaged you can repair it.

<http://www.quickpar.org.uk/>

Post by AndyHancock
How reliable is the zip that is native to Windows 7?

It's fine, as far as it goes. The zip spec has been around for a long time
and is well known, but it's subject to corruption from outside factors.
Tools like Quickpar address those weaknesses, whether for zip files or any
other type of digital file.

[Carson Chittom]

Post by Char Jackson
On Sun, 6 Jan 2013 13:51:53 -0800 (PST), AndyHancock

Post by AndyHancock
There have been times in the past when a zip file I created was
corrupt (or became corrupt somehow). I encountered this either using
WinZip or command-line zip, possibly in old Unix environments. To me,
there is a risk in relying solely on zip archives and deleting the
original unzipped files. The risk isn't only in losing one file that
is corrupt -- any corruption anywhere in the entire archive could
render all the files therein inaccessible. Hence, the risk increases
with the size of the archive.

If you're concerned with the integrity of any data files, zip or otherwise,
one way to get peace of mind is to use Quickpar to create a recovery set.
Normally, 10% is a nice round number to use, but feel free to adjust the
settings as you see fit. With a Quickpar recovery set, not only can you know
for sure whether your data is intact, but if it's damaged you can repair it.
<http://www.quickpar.org.uk/>

Post by AndyHancock
How reliable is the zip that is native to Windows 7?

It's fine, as far as it goes. The zip spec has been around for a long time
and is well known, but it's subject to corruption from outside factors.
Tools like Quickpar address those weaknesses, whether for zip files or any
other type of digital file.

In my experience the disk is more likely to be a problem than the
file--particularly optical disks. It's also worth mentioning the
obvious that for anything you really care about, you should back it up
in more than one place--and every so often, you should actually try to
restore--in a non-emergency way--from the backups you have, to make sure
they really are backups and not random bits.

[Char Jackson]

Post by Carson Chittom

Post by Char Jackson
On Sun, 6 Jan 2013 13:51:53 -0800 (PST), AndyHancock

Post by AndyHancock
There have been times in the past when a zip file I created was
corrupt (or became corrupt somehow). I encountered this either using
WinZip or command-line zip, possibly in old Unix environments. To me,
there is a risk in relying solely on zip archives and deleting the
original unzipped files. The risk isn't only in losing one file that
is corrupt -- any corruption anywhere in the entire archive could
render all the files therein inaccessible. Hence, the risk increases
with the size of the archive.

If you're concerned with the integrity of any data files, zip or otherwise,
one way to get peace of mind is to use Quickpar to create a recovery set.
Normally, 10% is a nice round number to use, but feel free to adjust the
settings as you see fit. With a Quickpar recovery set, not only can you know
for sure whether your data is intact, but if it's damaged you can repair it.
<http://www.quickpar.org.uk/>

Post by AndyHancock
How reliable is the zip that is native to Windows 7?

It's fine, as far as it goes. The zip spec has been around for a long time
and is well known, but it's subject to corruption from outside factors.
Tools like Quickpar address those weaknesses, whether for zip files or any
other type of digital file.

In my experience the disk is more likely to be a problem than the
file--particularly optical disks.

Optical disc issues are included in what I said above. If the optical disc
develops a problem, it's still the files that are affected. Tools like
Quickpar will let you know whether the files are ok, and if not, whether
they can be repaired.

Post by Carson Chittom
It's also worth mentioning the
obvious that for anything you really care about, you should back it up
in more than one place--and every so often, you should actually try to
restore--in a non-emergency way--from the backups you have, to make sure
they really are backups and not random bits.

If you use a tool like Quickpar, (I feel like I'm preaching by now, but it's
the most widely used and therefore the best example), you don't have to
actually unzip anything. You can just run an integrity check and be done
with it.

[glen herrmannsfeldt]

Post by AndyHancock
There have been times in the past when a zip file I created was
corrupt (or became corrupt somehow). I encountered this either using
WinZip or command-line zip, possibly in old Unix environments. To me,
there is a risk in relying solely on zip archives and deleting the
original unzipped files. The risk isn't only in losing one file that
is corrupt -- any corruption anywhere in the entire archive could
render all the files therein inaccessible. Hence, the risk increases
with the size of the archive.

For tgz, the usual unix gzipped tar file, any corruption makes it
pretty hard to recover anything after that.

As I understand zip, though, each file is compressed separately.
The index is at the end, and could be lost or corrupt, but it is usually
possible to find the beginning of a file, and uncompress it, even
without the index.

Post by AndyHancock
How reliable is the zip that is native to Windows 7? In addition to
that general question, what about specifically for files in the
Gigabyte range (fraction of a GB or several GBs)? If it is very
reliable, then I will use the Windows 7's "compressed (zipped) folder"
to create archives for writing to DVD.

You mean how often does it create corrupt zip files?

I would expect more often the corruption occurs later.

You could store them on a RAID (redundant) disk to reduce the corruption
that could happen.

-- glen

[BGB]

Post by glen herrmannsfeldt

Post by AndyHancock
There have been times in the past when a zip file I created was
corrupt (or became corrupt somehow). I encountered this either using
WinZip or command-line zip, possibly in old Unix environments. To me,
there is a risk in relying solely on zip archives and deleting the
original unzipped files. The risk isn't only in losing one file that
is corrupt -- any corruption anywhere in the entire archive could
render all the files therein inaccessible. Hence, the risk increases
with the size of the archive.

For tgz, the usual unix gzipped tar file, any corruption makes it
pretty hard to recover anything after that.
As I understand zip, though, each file is compressed separately.
The index is at the end, and could be lost or corrupt, but it is usually
possible to find the beginning of a file, and uncompress it, even
without the index.

it is also (often) possible to recover files from chunks of multi-part
ZIP archives, if the person knows how to do so...

there is a problem though that some tools are stupid and will make no
attempt to access an archive if they can't find the "end of central
directory" marker, but this is more of a problem of stupid tools than
the ZIP format itself.


this is partly because the ZIP format compresses each file separately,
and actually stores information about each file in several locations:
directly preceding the compressed file data;
in the central directory (stored at the end of the archive).

more so, each entry also has a nifty magic-code which can be used for
resynchronization.


note though that one thing which may often irreparably foul up ZIP
archives is LF <-> CR-LF autoconversion, which can happen sometimes.
this was often as a result of buggy FTP software (which mistakenly
identified a binary file as text), or occasionally brain-damaged
filesystem code (such as cases of UMSDOS auto-conversion being enabled).

(possibly as a result) some formats (such as PNG) include special logic
to at least detect if the file has gotten screwed up by such a conversion.

Post by glen herrmannsfeldt

Post by AndyHancock
How reliable is the zip that is native to Windows 7? In addition to
that general question, what about specifically for files in the
Gigabyte range (fraction of a GB or several GBs)? If it is very
reliable, then I will use the Windows 7's "compressed (zipped) folder"
to create archives for writing to DVD.

You mean how often does it create corrupt zip files?
I would expect more often the corruption occurs later.
You could store them on a RAID (redundant) disk to reduce the corruption
that could happen.

yep.

although, ironically, while raid protects fairly well against physical
failure of disks, it (sadly) generally lacks any protection against
OS-induced corruption (such as cases where the OS kernel gets corrupt
somehow and manages to go berserk somewhat before finally crashing /
blue-screening...).

often following these events, files would often be "sliced and diced",
often with contents of one file being mixed in with another, ...


this partly gave me a mistrust of NTFS on WinXP computers, partly as
IME, NTFS drives seemed to get fouled up by crashes a lot more often
than FAT32 drives.

luckily, this issue seems to have largely gone away AFAICT in Vista and
Win7.


for external archiving, it is a tradeoff...
I have often found the long-term reliability of CD-R and DVD-R's to
sometimes be a bit lacking...

granted, even as such, they still seem to hold up better IME than old
HDDs. if an HDD is left sitting unused for a number of years, often
either the spindle is stuck (so it can't spin up) or the contents are
otherwise corrupt/unreadable.

OTOH, IME, HDDs seem to last a lot longer when used occasionally, as
this seems to keep the spindles from seizing, and causes data to
regenerate (I suspect because HDDs will read and rewrite sectors to help
keep their contents from degrading and similar).


usually, at least some contents can be recovered from an old CD-R, but
not a whole lot can be recovered from a seized HDD...


or such...