Compression issue with large archive of files in DotNetZip

Question

Greetings....

I am writing a backup program in c# 3.5, using hte latest DotNetZip. The basics of the program is to be given a location on a server and the max size of a spanned zip file and go. From there it should traverse all the folder/files from the given location and add them to the archive, keeping the exact structure. It should also compress everything down to a reasonable amount. A given uncompressed collection of folders/files could easily be 10-25gb, with the created spanned files being limited to about 1gb each.

I have everything working (using DotNetZip). My only challenge is there is little to no compession actually happening. I chose to use the "AddDirectory" method for simplicity of code and just generally how well it seemed to fit my project. After reading around I am second guessing that decision.

1. Given the below code and the large amount of files in an archive, should I compress each file as it is added to the zip? or should the Adddirectory method provide about the same compression?

2. I have tried every level of compression offered by Ionic.Zlib.CompressionLevel and none seem to help. Should I think about using an outside compression algorithm and stream it into my DotNetZip file?

using (ZipFile zip = new ZipFile())  
{  
  zip.AddDirectory(root.FullName);  

  if (zipPassword.Length > 0)  
    zip.Password = zipPassword;  

  float size = zipGbSize * 1024 * 1024 * 1024;  

  zip.CompressionLevel = Ionic.Zlib.CompressionLevel.BestCompression;  
  zip.AddProgress += new EventHandler<AddProgressEventArgs>(Zip_AddProgress);  
  zip.ZipError += new EventHandler<ZipErrorEventArgs>(Zip_ZipError);  
  zip.Comment = "This zip was created at " + System.DateTime.Now.ToString("G");  
  zip.MaxOutputSegmentSize = (int)size;   //in gig  
  zip.Name = archiveDir.FullName + @"\Task_" + taskId.ToString() + ".zip";  
  zip.Save();  
}  

Thank you for any help!

Answer 1

Im not sure to have understated your question, but the maximum size for any zip file its 4Gb. Maybe you have to create a new ZipFile every time you reach that limit.

Sorry if that doesnt help you.