Concerns with compressing sensitive data in OSX

Question

I have some really sensitive data that I am trying to compress and back up so I can reformat. It's absolutely imperative that nothing happens to these files. I'm a developer so I have very little room for error... plus I'd really hate it if any of my .mp3's got corrupted!

File Formats Include...

• .mp3
• .php
• .js
• .ai - .psd - .flv

(and many more)

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1. Is the mac OSX file compression safe enough? Or should I look elsewhere?
2. Is there a more efficient/secure file-format other than .zip (i'm assuming so...)

Answer 1

I guess I'll answer the question for real (instead of complaining in the comments):

IMO, as long as you're transferring the data to your external storage medium appropriately, then any compression should be adequate. But, if you really want to ensure data integrity, I would do this:

1. Compress your data with SimplyRAR (free) however you choose, splitting the archive every 100MB or so (you want to have a decent amount of files, 30 should suffice depending on how much data you have). The files will be archive.rar, archive.r01, archive.r02 etc.
2. Use MacPAR deLuxe (also free) to create a few .PAR2 files for your archive. These files will allow repair and recovery of the archive if any parts are missing or corrupted.

This same strategy is used often on Usenet where files are often incomplete or missing from .rar archives. It allows for decent compression (not as great as lzma or 7zip, but pretty good) and good data integrity with the .par2 files.

When you extract your data, you can use my personal favourite UnRAR program for OS X, UnRARX. By double-clicking on the .par2 files (in the same directory as the .rar files), UnRARX will check the integrity of the files using the PAR data. This ensures that everything is exactly as you compressed it. Hope this helps with your decision!

Edit: Like I mentioned in my comment, compressing the .mp3 (and .flv) files won't do much to save space, but you do get the data integrity PAR provides. I'd just throw your whole ~/ folder into the archive.

Answer 2

This depends a great deal on why you need to bother compressing your data. If you don't have enough space lossless compression might not be sufficent to free up much storage as most of your data is probably contained in those mp3 and flv files. In this situation you might want to consider reencoding some of those files. However, if you have enough non-video/audio files to make compression worthwhile you have a great many options.

Perhaps the friendliest would be to use disk utility to create a compressed disk image on your destination drive. It's likely you'll want to make it large enough to fill up all the availible space on that drive. If all the data you need to save is in one directory you can make it even easier by simply selecting new disk image from directory from the file menu in disk utility. This is simple, easy and quite safe. You have a choice of compression formats. bzip will save you a bit more space at the cost of substantially increased compression time.

Since you say the data is sensitive this approach might appeal to you as you can also choose to encrypt the disk image using AES at the same time (it will ask you if you want to encrypt the image).

If you really really want to maximize your lossless compression install the paq8 command (say using macports or search on google) as that compressor tends to top the rankings.

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Finally if you need to compress application bundles and the like snow leopard has a neat feature that lets you keep them compressed and decompress them on the fly. This can even improve performance but to compress anything more than the precompressed apple applications you need to get the command line tool afsctool.