NOVELL TECHNICAL INFORMATION DOCUMENT

TITLE:  ReadMe for NW4DFS.EXE
README FOR:  NW4DFS.EXE

NOVELL PRODUCTS and VERSIONS:
NetWare 4.1

ABSTRACT:

Released patch of the NetWare Direct File System.


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ISSUE: 

Fix #1
 Problem: A problem occurs when a DFS file size is increased and the newly
acquired block was recovered from a recently deleted file still being
represented in the NetWare disk cache and is marked as dirty (or needs to be
written to disk), and the cache block is written to by DFS before the cache
subsystem performs it's periodic update. The effect is that if the newly
expanded DFS file area is written to and then read back, the read data will not
match the written data.

 Detail: Opening a file in DFS mode evacuates that file from NetWare cache. New
disk blocks are acquired as the DFS file size is increased. New disk blocks are
acquired from a list of free blocks. The disk blocks on the free block list
either never been assigned to any file, or they are recovered from deleted
files. Blocks from recently deleted files may still be represented in cache.

 Solution : This has been fixed by having DFS verify that newly acquired
blocks, obtained while expanding a file, are evacuated from the NetWare disk
cache.


 Fix #2
 Problem: A problem occurs when a DFS file size is increased and written to in
a non-sequential mode, causing the formation of a sparse file. The effect is
that data previously written to the to the DFS file might be zeroed out by
subsequent writes to adjacent blocks.

 Detail: It is possible write to a file in DFS mode in a manner that causes the
file to become a NetWare sparse file (ether by creating a new file or extending
an existing file). As a security measure, the newly acquired disk blocks are
zeroed out before use.

 Fixed: This problem has been fixed by changing the method of zeroing out the
newly acquired disk blocks.




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 Technology Background:
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 NetWare Disk Caching Subsystem Description

 NetWare's disk caching subsystem technology decreases data access time for
frequently accessed disk data. The technology involves storing a representation
of disk in the (RAM) memory of the NetWare file server.

 When a client reads and writes files that are stored on a NetWare file server,
the data does not interface directly with the server's disk storage hardware,
it is accessed in the file server's memory cache (RAM). NetWare periodically
updates the disk storage hardware as needed.


 NetWare Direct File System

 The Direct File System (DFS) allows an application to bypass the NetWare Disk
Cache and Transaction Tracking Systems. DFS is necessary for some database
applications that provide their own caching and transaction tracking
facilities.

 Backup applications often access large amounts of data not being accessed by
other applications. If these accesses are made through the cache, the cache
becomes non-relevant for all other accesses, and general server performance
suffers from other users.

 Some utilities may also require the ability to specify exactly where files are
placed, so that volumes can be de-fragmented and optimal file access can be
made.

 NetWare does not allow a file to be opened in both the cache and DFS modes
simultaneously. DFS file open requests can only be made by an NLM application,
and fails if the specified file is already open by any other (NLM or NetWare
client) entity. While a particular file is opened in
 DFS mode, NetWare will deny all other open requests (for both DFS and cache
modes) for that file.

 Files opened in DFS mode must not have any portion represented in NetWare
cache. Therefore, as the file is opened in DFS mode, NetWare searches all cache
for blocks that belong to the file. If a cache block belonging to the file
being opened is encountered, the cache block content is written to the server's
disk storage hardware (if required), and the cache block is disassociated from
the file being opened.  This process may take considerable time, depending on
the size of the
 file being opened in DFS mode, and the total number of cache blocks in server
RAM.


 NetWare Sparse Files

 The NetWare file system allows the creation of what Novell calls "sparse
files." A sparse file is a file which has "holes" or areas which have not been
yet been written to.  A sparse file is formed by opening a new file writing to
it non-sequentially.

 An example of a sparse file is one where the file is opened, and data is
written to the file starting at offset 1000 and then closing the file. In this
state, the file offsets 1 through 999 have not been written to and represents a
hole in the data of the file. If an attempt is made to read from offset 1
through 999, NetWare returns zeros as the data.

 NetWare only allocates disk blocks to portions of a sparse file that have been
written to. NetWare does not allocate disk blocks to a sparse file's holes.


Self-Extracting File Name: NW4DFS.EXE

Files Included     Size     Date      Time

..\
      NW4DFS.TXT     (This file)
    DFSCCHFX.NLM            2219        10-18-96     10:44:04 pm
    DFSSETFX.NLM            5783        10-18-96     11:34:46 pm


Installation Instructions:

1. You need to have previously installed the NetWare 4.10 patch kit
(410PT6.EXE) which includes the patch manager (PM410.NLM). The patch manager
must be loaded in order to add NetWare server operating system patches.

 2. Copy the DFSSETFX.NLM and DFSCCHFX.NLM files into the patches directory on
the servers boot drive (C:\NWSERVER\PATCHES\410PT6\NATIVE\START_PT).

 3. Down and restart the file server.



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