Re: Data compression and stuff, was Re: [SLUG] Backup options

[Matt Hyne <mhyne@xxxxxxxxx>]

Serious backup solutions do not use compression at all, since 

1. If the data is corrupted on the tape it is much more difficult to extract the remaining uncorrupted data if the whole archive has been compressed.
2. It gives you a variable tape capacity - that is, you never know how much you can fit on the tape before it runs out - a 20Gb/40Gb backup device is really a somewhere between 20-40Gb depending on the data being saved.

Matt

At Thursday, 8/11/2001 11:33 AM (+1100), Terry Collins wrote:


>> 1. Ensure that data compression is turned on on the HP tape drive (I've just
>> gone through this myself)
>> 
>> 'mt -f  /dev/st0 datcompression' will give you this (assuming the tape is
>> /dev/st0)
>
>I'm after some clarification for better understanding here on
>compression. My understanding is that you can either choose software or
>hardware compression[1].
>
>Then the degree of compression you get depends on the compressibility of
>the data(files). So when I am only getting 14-15Gb on my DDS3 tapes
>(12/24Gb), it is because my data(files) are not that compressible.
>
>As I understand it, the 24Gb comes from the old rule of thumb that text
>documents could be compressed to about half size to save space.
>
>[1] The mathematicians can argue which is best, but it was really horses
>for courses. Software was generally seen as better because it could be
>updated to a better algorithm, but hardware was locked to the hardwired
>algorithm.
>
>
>
>-- 
>   Terry Collins {:-)}}} Ph(02) 4627 2186 Fax(02) 4628 7861  
>   email: terryc@xxxxxxxxxx  www: http://www.woa.com.au  
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