Error in NTBackup when backing up large drives to compressed folder

From: Ken Levy (nospam_at_nowhere.com)
Date: 04/17/04 

Date: Sat, 17 Apr 2004 06:05:41 -0500

We are using NTBackup to create backups of user and server hard drives onto
large (>200 GB), inexpensive IDE hard drives in removable drive carriers.
This procedure has worked very well for us with one exception.

To optimize the space on the backup hard drive, we set up the target
directory (which receives the *.bkf file) as compressed.

We have one shared server hard drive that has over 50 GB of data on it.
When we run NTBackup (Win2000 Professional with all the latest Windows
Updates applied) on this drive, we get the following messages:

  Error: The device reported an error on a request to write data to media.
  Error reported: Unknown error.

These errors appear after the backup has been running 4 hours + and has
backed up 45,764,258,290 bytes. After further investigation, we found that
the backup file (*.bkf) created by the routine showed the following
filesizes (as reported by Windows Explorer):

Size: 42.6 GB (45,812,942,848 bytes)
Size on disk: 30.4 GB (32,688,783,360 bytes) (Note: target directory is
compressed)

My questions are as follows:

1) Is there a maximum compressed file size of 32GB on the media (I wasn't
able to find anything in the KB documenting such a restriction)?

2) Is this a bug or documented restriction in NTBackup?

3) Is there a command line switch in NTBackup to compress the output stream
when using disks as the target output device? The only one I could find
only works with tape devices. The only way we found to get compression on
disk was to set up the target's directory as compressed, in advance.

Given the falling prices, increasing capacities, removeability (via USB2.0
or IEE1394) and higher speed / reliability of IDE hard drives (versus tape),
I think we will be seeing more and more people switching over to disk based
backup media from tape, and resolving this issue will be important.

TIA for any comments, fixes, etc.

Please post any responses to the newsgroup.

Note: Cross-posted in microsoft.public.win2000.file_system 

-- 
Ken

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