Browse Prior Art Database

386 High Performance File System Threshold Readahead

IP.com Disclosure Number: IPCOM000106697D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Knox, T: AUTHOR [+3]

Abstract

Disclosed is a read ahead method that maximizes cache hits and minimizes disk access delays. This method is used by 386 High Performance File System (386 HPFS), as packaged in the IBM OS/2 LAN Server 2.0* product.

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386 High Performance File System Threshold Readahead

      Disclosed is a read ahead method that maximizes cache hits and
minimizes disk access delays.  This method is used by 386 High
Performance File System (386 HPFS), as packaged in the IBM OS/2 LAN
Server 2.0* product.

      Read ahead is a performance enhancing scheme used by file
systems.  When a file is being accessed sequentially by an
application, the file system will read ahead of the application,
storing the additional file data in a cache buffer.  When the
application requests that data, the file system simply has to return
the data out of cache (a memoryaccess), instead of going to disk.
Read ahead can be done synchronously (i.e., reading more data off
disk than what the application requested, storing the extra data in
cache, then returning to the application with its requested data), or
asynchronously (i.e., before returning to the application with its
data, queue a disk request for more data, with this request
completing sometime in the future, optimally before the application's
next request).

      Prior to this invention, 386 HPFS used an asynchronous read
ahead for a data amount equal to the application's request size.  For
example, when an application requested 2K bytes (2KB) of data, 386
HPFS would first read that 2KB into cache, and before returning to
the application with that data, it would queue a read request to disk
for the next 2KB of data.

The disadvantages of the old 386 HPFS read ah...