Storage Optimization

Can You Compress Already Compressed Files? Part II

Posted in Featured,File Systems,Storage by storageoptimization on May 6, 2008

In my last post I discussed the fact that most files that are used are already compressed. And up to now, there were no algorithms to further compress them. Yet, it’s obvious that there needs to be a new solution.

On the cutting edge, there are some new innovations in file-aware optimization that allow companies to reduce their storage footprint and get more from the storage they already have. The key to this is understanding specific file types, their formats, and how the applications that created those files use and save data. Most existing compression tools are generic. To get better results than you can get with a generic compressor, you need to go to file-type-aware compressors.

There’s another problem. Let’s say you just created a way better tool for compressing photographs than JPEG. That doesn’t mean your tool can compress already-compressed JPEGs, it means that if you were given the same original photo in the first place, you could do a better job. So the first step in moving towards compressing already-compressed files is what we call Extraction – you have to extract the original full information from the file. In most cases, that’s going to involve de-compressing the file first, getting back to the uncompressed original, and then applying your better tools.

Extraction may seem simple enough – just reverse whatever was done to a file in the first place. But it’s not always quite that easy. Many files are compound documents, with multiple sections or objects of different data types. A PowerPoint presentation, for example, may have text sections, graphics sections, some photos pasted in, etc. The same is true for PDFs, email folders with attachments, and a lot of the other file types that are driving storage growth. So to really extract all the original information from these files, you may need to not only be able to decompress files, but to look inside them, understand how they are structured, break them apart in to their separate pieces, and then do different things to each different piece.

The two things to take away from this discussion are: 1) you won’t get much benefit from applying generic compression to already-compressed file types, which are the file types that are driving most of your storage growth and 2) it is possible to compress already-compressed files, but to do so, you have to first extract all the original information from them, which may involve decoding and unraveling complex compound documents and then decompressing all the different parts. Once you’ve gotten to that point, you’re just at the starting point for where online data reduction can really get started for today’s file types.


One Response to 'Can You Compress Already Compressed Files? Part II'

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  1. draft_ceo said,

    At what speed do your optimizers/readers run at? What is the impact on the target storage devices while compression is going on? Are you doubling/tripling the load on the target devices?

    In fact, is it not better to build this functionality on the target storage device? That will allow much more flexible compression scheduling polices, etc.

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