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STACKER NOTE                                                   STACKER NOTE
Title: Third Party Disk Optimization Programs and Stacker 
STAC FAX Index #2402 - 2/10/93                          
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Background.

Writing to disk can cause file fragmentation over time.  Third party 
disk optimization programs such as Norton Speedisk, PCtools Compress, and 
VOPT were designed to optimize (defragment) un-Stacked drives.  Their use 
on Stacker drives should be avoided.  Stacker includes a utility called 
SDEFRAG to optimize and defragment a Stacker drive.  Note: SDEFRAG will not        
optimize an un-Stacked drive. 


Why shouldn't I run third party optimizers on a Stacker drive?
   
   Stacker is able to store data more efficiently than DOS by allocating 
   file storage units at the sector level.  A sector, usually 512 bytes, is 
   the smallest unit of storage that a hard disk controller can write.  
   DOS, on the other hand, uses fixed size, multi-sector groups (clusters) 
   for file allocations.   A cluster, typically a group of 4 sectors for 
   partitions under 128 MB, is the smallest unit of storage used by DOS.  
   While DOS uses a File Allocation table (FAT) to allocate the cluster usage 
   in a drive, Stacker keeps both a cluster FAT and a sector FAT.  
   An Optimization program will read the FAT to find all the file fragments, 
   then put the pieces together using contiguous clusters.  Since DOS doesn't 
   keep track of individual sectors like Stacker does, these programs, which 
   existed long before Stacker came along, were designed to read only a 
   cluster FAT.  They were not designed to read a sector FAT.  This is why 
   they should not be used on the Stacker drive.  

What if I accidentally run a third party optimizer on a Stacker drive?

   Because these programs don't read Stacker's sector FAT, they tend to
   fragment a Stacker drive as they assemble the file's pieces in what they
   think is a contiguous order.  The data remains safe, however, the 
   optimization process may have created lost sectors.  Run the Stacker 
   utility :   SCHECK /F (Stacker 2.0) or CHECK /F (Stacker 3.0)  to reclaim 
   these lost sectors.  Then run SDEFRAG to defragment the drive.

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Copyright 1993, Stac Electronics