AN MS-DOS FILE SYSTEM FOR UNIX
Alessandro Forin
Gerald R. Malan
School of Computer Science
Carnegie Mellon University
Pittsburgh, Pennsylvania 15213
Abstract
We have written DosFs, a new file system for UNIX that uses MS-DOS
data structures for permanent storage. DosFs can be used anywhere a
traditional UNIX file system can be used, and it can mount disks
written by MS-DOS as regular UNIX partitions. DosFs can be used as
the root partition, and exported by an NFS server. Our motivation for
this work was efficient disk space utilization; DosFs provides from
30% to 80% better disk utilization than the 4.3 BSD Fast File System
(FFS). In addition, we found that the disk block allocation algorithm
used by DosFs lets us exploit large contiguous disk operations,
providing a five-fold improvement over FFS for uncached operations.
To the best of our knowledge, this is the first file system
implementation that allows the user to specify the logical block size
at mount time. A user can mount the same fileystem with a larger
block size when file accesses tend to be sequential and a smaller one
when they tend to be scattered. The MS-DOS structures were designed
for a single-user system and do not support access control. We solved
this problem with simple extensions that are backward-compatible with
MS-DOS.
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