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markm75

0% compression on a backup?

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I'm running version 7.6 doing backups to an external harddrive.. for some reason it isnt getting any compression at all.. at the end it says 0% compression..

 

Any thoughts on how to get this working?

 

Thanks

 

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That is an overall average and is sometimes not very accurate. If you get properties on each file in the session contents report it will show you the % of compression for that specific file. You may have mostly files that do not compress very well.

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Well i know its not compressing at all.. as i see the original file size tally.. and then do a property check on the backed up files.. they match, 0% compression..

 

Which is a bit of a let down, considering i know i was getting at least 30% using other solutions out there.. (same files backed up)

 

I guess there is nothing i can do to tweak this?

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It depends on the content of your files. Are they already compressed? Are they file formats like JPG or MP3 which are inherently compressed already? Are you backing up to tape and have hardware compression enabled?

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They are a mixture of everything really.. its on an external harddrive via esata..

 

Again, this same data, backed up using acronis would compress very nicely.. say 20-30%.. vs 0% here so far..

 

 

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I have the same problem. After making backup of my user data folder i get 0% compression. Acronis True Image gives me 30% compression of the same files. There are many files which can be compressed well. Where is the problem?

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This may just be how the total is displayed in the log. If you get properties on individual files in the reports>Session contents browser, it will show you compression rates for each individual files.

 

Also, image based backup will compress differently then a file by file backup like Retrospect.

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Some tests:

 

1. Folder of text files (about 1GB) on my desktop filled with "0" has 99% compression in Retrospect. File backup set, compression and encryption AES128 enabled. Resulting .rbf file is 1 512 KB. This is OK

"Completed: 58 files, 928,2 MB, with 99% compression"

 

2. Backup of My documents and Settings/Username profile, 3,95GB of files *including* 1GB folder of files filled with "0" on my desktop (File backup set, compression and encryption AES128 enabled):

"Completed: 9747 files, 4,0 GB, with 11% compression"

resulting bkf file is 3,68GB.

1GB of those files are files filled with "0", compression ratio should be more than 20% and resulting file should be smaller than ~3GB. I can see in session contents that my files filled with "0" have 99% compression so why the resulting backup file is so big?

 

 

3. Backup of My documents and Settings/Username profile to a *new backup set* after deleting the files filled with "0"

"Completed: 9700 files, 3,1 GB, with 0% compression"

and the backup set file is 3,68GB!

After checking random files in the session browser I can see that the files actually *are* compressed more or less so the backup set file should be less than 3,1GB. Some files don't show compression ratio.

 

The file is just as big as file after backup of dummy "0" files in point 2. It looks like the files actually were 99% compressed but something is adding some data to the backup set.

 

 

4. Backup of my My documents and Settings/Username profile to a new backup set *without compression*:

Completed: 9702 files, 3,1 GB

and the backup file is 3,2GB.

Backup without compression is actually smaller than backup with compression!?

 

To check if my user profile can be actually compressed I have compressed the resulting file with winrar using fastest compression with smallest compression ratio. Backup set was compressed to a 8% smaller file. Acronis True Image can compress my profile with about 30% ratio when using the maximum compression level. I'm using it in file backup mode, not image mode, actually image backup should be bigger because additional data would be added.

 

5. Backup of folder with ~1G of already compressed data to check if Retrospect is not adding big amount of data to already compressed files when using it's own compression.

Completed: 760 files, 945,6 MB, with 0% compression

Backup file is 1,42GB. It looks like Retrospect is adding really big amount of data to already compressed files. Modern compressors also add data to already compressed files but it's a small amount of data. With 760 of ~1,2MB files it should not be nowhere near 0,6MB per file. It's 50%! I have read that Retrospect is using it's own proprietriary compression format, it looks like it's the cause.

 

 

 

Another thing is that some files in session contents don't show compression ratio in properties. Only file size. Those files are already compressed like the ones I mention above. Not a single compressed file is showing it's compression ratio! It only states something like 1 874 total (1 303 885 bytes used) and the size kolumn shows 1 274 K. Why compression ratios are hidden for those files?

 

It looks like Retrospect is hiding those informations on purpose. It should clearly state how much data it's adding to backups with compressed files.

 

I have a copy of Retrospect Express but it has only it's proprietriary encryption that is weaker than DES. So i'm testing the Pro version because it has AES and now this. I'm starting to get angry really. It looks like Retrospect is making things worse with it's proprietriary compression algorithm. Compression is a basic functionality, even free programs work better!

 

Do you have any explanations?

 

 

 

 

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Another thing is that some files in session contents don't show compression ratio in properties

 

Many files are pre-compressed (digital video/audio, etc) and those files can not be compressed. Retrospect uses a filter to exclude these types of files from being compressed. Compressing a pre-compressed file will make it larger.

 

 

 

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1.Retrospect is still compressing already compressed files. I have demonstrated it and you can check it yourself!

 

2.There is no modern compression tool that adds 50% data when compressing already compressed file. Just compress something with ZIP two times. The file is bigger but it's not even 1% bigger.

 

Retrospect is adding 50% data to already compressed files like you can see in my previous post!

 

 

Compression algorithm used by Retrospect is clearly outdated. Just like encryption algorithms used in Retrospect Express.

 

I'm using EMC Legato NetWorker where I work for backup of servers and it works really good. Buy I'm not very impressed with Retrospect.

 

Are you going to do something with it or just leave it so?

 

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Looks like Retrospect because of no obvious reason disable software compression without a notice, when no encryption is used (I assume Retrospects consider that hardware compression is present). I suggest you may circumvent the problem by setting encryption for the Backup Set. This disables the hardware compression, thus software compression is back.

Strange that EMC do not recognize the problem.

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I have 7.6.2.101 and got 2% compression backing up two separate volumes to a file on a network drive. I used to see 15 to 30% on older versions of retrospect.

 

I don't want to encrypt just to get compression.

 

Hey EMC... Something seems broke here.

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Compression is ALWAYS based on the type of file you copy. The % is an average.

 

Go to Reports>Session Contents and get properties on a random file. The % of compression for that file will be displayed. All pre-compressed file types we know about are excluded from the compression process.

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1.Retrospect is still compressing already compressed files. I have demonstrated it and you can check it yourself!

 

It has to be a "known" pre-compressed file type. If we don't know about the file extension being pre-compressed then we will try to compress it. See the above steps to see if your file is being compressed by Retrospect.

 

The above is for software compression only.

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The problem is that Retrospect is adding 50% of additional data to already compressed files.

 

Excluding compressed files is not needed if the compression algorithm is decent because it will not add that amount of data. Even the most simple compression apps add max 1%.

 

Every other backup program is compressing ALL files because even if every file in backup is already compressed it will add less than 1%.

 

 

Excluding compressed files in retrospect is just a dirty hack. You exclude files based on extension? It is USELESS!

 

When you will fix this? When you will add a DECENT compression algorithm? Why your algorithm is adding so much data to compressed files?

 

There is no modern compression algorithm that adds 50% of overhead even after compressing already compressed file 10 times!

 

When you will fix the algorithm?

Edited by Guest

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