title: Is it bad to 7zip SQL backups compressed using NTFS compression?
body: <p>I've been searching on the Internet for last week but I haven't found anything. I have such a problem:
  We have daily SQL backups in company starting from 2012 up to today. All those files are "compressed" using standard disk compression. </p>
  
  <p><a href="https://i.stack.imgur.com/dEz9x.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dEz9x.jpg" alt="enter image description here"></a></p>
  
  <p>It's about ~500 files per month. It's about 24 000 files. It's huge amount of disks space (every day cost about 9 gb now, 6 gb in 2012). And it's backup, so have those files in three different places.</p>
  
  <p>I want to 7z those files, because, for example, if database have 2 gb, after Windows disk compression feature it has ~1200 mb. When I 7z this file, it has 200 mb.</p>
  
  <p>I've made simple batch script that decompress those files, pack them and delete. After one day it has done one month. Decompressing cost much time. </p>
  
  <p>I see ziping sql BAK files is very common and safe. But now the real question is - do I have to decompress each file, and then pack it, or is it safe to 7z "compressed" files?</p>
  
  <p>Here is the script: </p>
  
  <pre><code>echo off
  FOR /R %%i IN (*.bak) DO ( 
  echo Decompressing %%i
  compact /u "%%i" &gt;&gt; log.txt
  ping 127.0.0.1 -n 2 &gt; nul
  echo Zipping %%i
  "C:\Program Files\7-Zip\7z.exe" a "%%i.7z" "%%i" &gt;&gt; log.txt
  echo Deleting %%i
  del "%%i" &gt;&gt; log.txt
  echo _____)
  </code></pre>