if i zip and unzip a file, is it as good as the original?

Discussion in 'OT Technology' started by dorkultra, Feb 6, 2010.

  1. dorkultra

    dorkultra OT's resident crohns dude OT Supporter

    Joined:
    Oct 14, 2005
    Messages:
    22,743
    Likes Received:
    27
    Location:
    yinzer / nilbog, trollhio
    i do nightly backups for my dad's dental database. its a couple hundred MBs. if i zip it with normal compression, it condenses it down to around 50 MB

    when i unzip the file, its the exact same file size. i'm wondering if there would be any loss/corruption of data on the unzipped file compared to the original

    the reason for this is because my dad's up speed on his dsl is pretty weak and it can take quite some time to transfer the files. compressing them first, downloading them to my server, and decompressing them cuts the time in half
     
  2. 5Gen_Prelude

    5Gen_Prelude There might not be an "I" in the word "Team", but

    Joined:
    Mar 14, 2000
    Messages:
    14,519
    Likes Received:
    1
    Location:
    Vancouver, BC, CANADA
    What would be the point of compressing the files if you couldn't expand them without fear of losing data?
     
  3. White Stormy

    White Stormy Take that, subspace!

    Joined:
    Sep 17, 2002
    Messages:
    85,489
    Likes Received:
    70
    Location:
    Sparkopolis
    yeah, but really you should transmit two backup copies.. one via internet/FTP/whatever you're doing and another on CD or USB or something.
     
  4. crontab

    crontab (uid = 0)

    Joined:
    Nov 14, 2000
    Messages:
    23,446
    Likes Received:
    12
  5. dorkultra

    dorkultra OT's resident crohns dude OT Supporter

    Joined:
    Oct 14, 2005
    Messages:
    22,743
    Likes Received:
    27
    Location:
    yinzer / nilbog, trollhio
    yeah, we do an uncompressed copy onto a flash drive and he brings it back home every night.
     
  6. Swerve

    Swerve OT Supporter

    Joined:
    Feb 20, 2005
    Messages:
    3,179
    Likes Received:
    3
    Look into MD5 Checksums for checking if one zip matches another zip
     
  7. CodeX

    CodeX Guest

    Or, just use winrar/winzip/any other utilities tool to do that automatically, like they all do to begin with and warn you if they don't match...
     
  8. dorkultra

    dorkultra OT's resident crohns dude OT Supporter

    Joined:
    Oct 14, 2005
    Messages:
    22,743
    Likes Received:
    27
    Location:
    yinzer / nilbog, trollhio
    yeah seems to be working fine. i tested the backup as well. however its a database, so some obscure table could get fucked up and you wouldn't know until you accessed it.

    his dental program comes with a data cleanup utility that verifies an rewrites everything. tests as good as the original

    i'm not sure how to compare hashes. i'm guessing that i'd need something like winzip.
    i've just been using the send to -> compressed file, using the built in windows xp zipping program
     
  9. Chris

    Chris New Member

    Joined:
    Oct 27, 2003
    Messages:
    14,711
    Likes Received:
    0
    Location:
    Texas on my mind
    If its only a couple hundred MBs does it really make that much of a difference whether it compressed or not? And what does the software manufacture say about compressing the database?
     
  10. CodeX

    CodeX Guest

    I would use winrar if I were you, it is free, and does this CRC check that we are talking about automatically, warning you if the compressed data does not exactly match the original... which never happens unless the resulting compressed file gets corrupted, but if that happens it would happen whether it was compressed on the disc or not.
     
  11. dorkultra

    dorkultra OT's resident crohns dude OT Supporter

    Joined:
    Oct 14, 2005
    Messages:
    22,743
    Likes Received:
    27
    Location:
    yinzer / nilbog, trollhio
    i didn't ask them...seems that i know more about the software than they do, the few times i've talked to them

    i guess i could just set it to upload to my server and walk away. just seems much quicker to compress and then upload
     
  12. CodeX

    CodeX Guest

    It is, and compression alone will never corrupt the data.

    Basically, if the compressed file gets corrupted it is likely the data would have gotten corrupted anyway, compressed or not.

    But, if you are really worried about that look into PAR2 and quickpar.
     
  13. HY

    HY New Member

    Joined:
    Dec 10, 2006
    Messages:
    57
    Likes Received:
    0
    yes the file as good as it was previous compression. there are two types lossless which is used with files such as zip, rar, .... and lossy which is best used with some types of media, mp3, divx, h264 ....
     
  14. retorq

    retorq What up bitch??

    Joined:
    Dec 14, 2006
    Messages:
    6,061
    Likes Received:
    0
    Location:
    Mohave Desert
    I've been gone for a few days, was this really a serious question??
     
  15. dorkultra

    dorkultra OT's resident crohns dude OT Supporter

    Joined:
    Oct 14, 2005
    Messages:
    22,743
    Likes Received:
    27
    Location:
    yinzer / nilbog, trollhio
    yes :wtc:
    appreciate all the help
     
  16. deusexaethera

    deusexaethera OT Supporter

    Joined:
    Jan 27, 2005
    Messages:
    19,712
    Likes Received:
    0
    I think LZW is also lossless compression. There are plenty of lossy compression algorithms, but only a few lossless compression algorithms. People only use lossy compression for data that you won't notice the loss of data in, like images, video, and audio.
     
  17. CodeX

    CodeX Guest

    I implemented a form of multidimensional RLE for a project at work... /bragging
     

Share This Page