Re: RAR under linux: any alternative?
Alex Malinovich wrote:
On Mon, 2005-12-12 at 21:47 -0600, Mike McCarty wrote:
--snip--
[snip]
To put it another way, are you aware that hard discs have redundancy
in them to allow one to recover corrupted sectors? By your reasoning,
this could not be put on the same disc, it would have to be on
another disc.
Yes, but CRC checks on packets of data (a few kilobytes at a time) are
much different than a checksum on a 10, 20, or 50 MB archive,
particularly when speaking in terms of a lower-bandwidth connection.
It's easy enough to resend a TCP/IP packet if the CRC check fails.
However, we want to AVOID resending a 50 MB file if the checksum doesn't
agree with the file. It's much easier to re-download a 1K checksum file
than a 50 MB archive.
WRT to your statement about hard drives, I believe the feature you're
referring to is the ability to ignore bad sectors, not recover data from
them. If the drive determines a particular sector to be bad, it will
mark it as being bad and write the data elsewhere. If the data has
already been written to a sector, and that sector subsequently goes bad
I'm not aware of any low-level features to allow the recovery of that
sector after the fact.
Yes, there are FEC redundancy bits put into them, such that a sector
can be read and the data corrected even in the face of errors.
--snip--
(1) the ability to open and extract files from previously created RAR
format archives, and (2) the exchange of files with people who as a
customary practice use that format for archiving and compression
and prefer to send and receive them in that format.
(1) unrar-free would do this as well
(2) see below
I can't control my neighbor's dog, let alone my neighbor. If
someone I am doing a contract for requests RAR format, then
that's what he'll get, and I won't argue. I consider putting
food on my table a very practical thing.
I completely agree. I'm not fortunate enough to be able to make a living
evangelizing free software either. (I work at a 99% MS shop. Used to be
100% until I got there, so I'm making inroads. :) )
However, the original question referred to how to archive a large amount
of data and split it into pieces for transferring to someone else. If
I answered your question as asked. I wasn't promoting RAR, I was
stating what RAR can do that nothing else can do. Personally, I've only
used it a few times, and didn't find it to be particularly better
or worse than other archival programs. Also, personally, I *dislike*
the *NIX world's most common technique of compressing entire
archives. This is the worst of all possible worlds, IMO. The way
ARJ, ZIP, etc. works is IMO far superior to the way "tar zf" works.
someone REQUESTS RAR specifically, and I have a business relationship
with them, I'll certainly oblige. However, if the format is unspecified,
as in this case it was, I would certainly choose to use free software to
do the job.
Glad to see that you retain your sanity, then. I recall a few
months ago when I needed to do some editing on my resume (don't
we all) in order to make a job app. I had a copy in Word
format, and so I wanted to edit it. But Open Office couldn't/
wouldn't save in Word format. The people I was making app to
had specifically requested Word format, so I asked for some help
on another mail echo. I got roundly lambasted by one guy who
wanted me to tell them how wrong they were to want Word format,
and said that so long as I "played their game" I was contributing
to Evil in the World.
Anyway, back to the topic.
If I needed to do that, and had complete freedom of choice in
how to do it, and were worried about getting corruption,
I'd do this...
For a Linux to Linux copy, I'd use tar or cpio to build a
single large archive. Then I'd split it. Then I'd compress
each of the pieces using gzip separately on the pieces,
and transmit them. I'd use the internal redundancy check
while decompressing to look for errors, and retransmit
the pieces which got corrupt. Then I'd concatenate the
pieces and use tar or cpio to recover the files.
Mike
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