Tape backup software with automatic compression?

Most hardware will recognize compressed files and not try to recompress
them. I would imagine software would do the same, but I never use it. What
exactly is your goal? Recompressing a zip will sometimes cause it to grow,
but not significantly. And you are mixing file compression with image
compression. They are not the same. A tif or jpg can still be compressed via
file compression, though not a lot. And they will not grow in size. And in
hardware compression (on newer drives anyway, i.e. AIT, SDLT), trying to
compress a compressed file doesn't decrease throughput to any significant
degree.


"Doug Warner" wrote in message
...

By "automatic compression", I mean that the backup software recognizes
filetypes that are already compressed, either by extension (jpg, zip),
or by content, in the case of .tif files, which may or may not be
compressed. The software should save all these types for last, and
turn off compression (software or hardware) before writing them.

So far, all I've found is SW that lets the user turn compression on or
off, so you have to do two separate backups, manually selecting the
folders/drives that contain each type of file.

Is there any software that will make my computer do this repetitive
task FOR me?

To reply, please remove one letter from each side of "@"
Spammers are VERMIN. Please kill them all.

In article zKsYd.71016$Tt.38626@fed1read05,
Steve Gavette wrote:
Most hardware will recognize compressed files and not try to recompress
them. I would imagine software would do the same, but I never use it. What
exactly is your goal? Recompressing a zip will sometimes cause it to grow,
but not significantly. And you are mixing file compression with image
compression. They are not the same. A tif or jpg can still be compressed via
file compression, though not a lot. And they will not grow in size. And in
hardware compression (on newer drives anyway, i.e. AIT, SDLT), trying to
compress a compressed file doesn't decrease throughput to any significant
degree.



"Doug Warner" wrote in message
.. .

By "automatic compression", I mean that the backup software recognizes
filetypes that are already compressed, either by extension (jpg, zip),
or by content, in the case of .tif files, which may or may not be
compressed. The software should save all these types for last, and
turn off compression (software or hardware) before writing them.

So far, all I've found is SW that lets the user turn compression on or
off, so you have to do two separate backups, manually selecting the
folders/drives that contain each type of file.

Is there any software that will make my computer do this repetitive
task FOR me?

To reply, please remove one letter from each side of "@"
Spammers are VERMIN. Please kill them all.



You're misinterpreting the compression feature in the software.
Turn it on and it tries to compress all files. There is no harm done
compressing a compressed file a second time in the backup software.

The tape drive will apply some stream compression algorithm
consistantly to the date stream when writing and the reverse algorith
when reading back. It doesn't know or care about the characteristsics
of the files it's handling. The compression percentage depends on the
data. text files compress big-time (i've seen 20:1) and zip files
won't compress at all but it's all automatic.

If you're using NTFS filesystem with the compression property turned
on the OS decompresses the file in the file system drivers and send
the expanded data to the tape drive controller which will compress it,
again and reverses the steps when rading. It's all transparent.

--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

In article ,
Doug Warner wrote:

By "automatic compression", I mean that the backup software recognizes
filetypes that are already compressed, either by extension (jpg, zip),
or by content, in the case of .tif files, which may or may not be
compressed. The software should save all these types for last, and
turn off compression (software or hardware) before writing them.

So far, all I've found is SW that lets the user turn compression on or
off, so you have to do two separate backups, manually selecting the
folders/drives that contain each type of file.

Is there any software that will make my computer do this repetitive
task FOR me?

To reply, please remove one letter from each side of "@"
Spammers are VERMIN. Please kill them all.

Not that I know of. The best compression is done by tape drives that
offer hardware compression built in and most modern tape drives offer
that feature. I back up a few terabytes per night over 14 tape drives in
two tape libraries and we turn software compression off and just let the
hardware compression do the job.

Doug Warner wrote:
By "automatic compression", I mean that the backup software recognizes
filetypes that are already compressed, either by extension (jpg, zip),
or by content, in the case of .tif files, which may or may not be
compressed. The software should save all these types for last, and
turn off compression (software or hardware) before writing them.

So far, all I've found is SW that lets the user turn compression on or
off, so you have to do two separate backups, manually selecting the
folders/drives that contain each type of file.

Is there any software that will make my computer do this repetitive
task FOR me?

To reply, please remove one letter from each side of "@"
Spammers are VERMIN. Please kill them all.

I use afio which will compress each file separately (best way for backups).
It takes a list of extensions to not compress.

$ afio -E /backup/afio.ext ...

and afio.ext has:
..bz2
..zip
..gif
..jpeg
..jpg
.... and so on.

About compressing already compressed files: I found it to be a real
problem. Hardware compression was significantly expanding my already
compressed files (this is in the DAT2 days). I turned it off and let
my CPU (afio in this case) take care of compression.

--
Eyal Lebedinsky ) http://samba.org/eyal/
attach .zip as .dat