Gospel of Caching According to Max

By popular demand! The following "Gospel of Caching According to Max" is provided by Proportional Software based upon a great deal of OS/2 system "tweeking" done by the DCF/2 development team.

You can get better performance from your system by using the memory you have available to you in the most efficient and effective way.

From the table below, select the case that best describes the file system or systems you use and memory available on your system.

CASE 1: You use only HPFS or only FAT but not both. HPFS only                        FAT only

If system memory is at least:   Set CACHE: to                  Set DISKCACHE: to                         16 MB         2048                             2048 12 MB        1536                             1536 8 MB        1024                             1024 Set FAT DISKCACHE Parameters: LAZY WRITES                 N/A                               LW

Set HPFS CACHE Parameters: LAZY WRITES               /LAZY:ON                           N/A MAXAGE                >7,500                            N/A DISKIDLE                60,000                            N/A BUFFERIDLE                60,000                            N/A

If your system is HPFS only REM out the DISKCACHE statement in your CONFIG.SYS file. If your system is FAT only, REM out the IFS=HPFS.IFS statement.

CASE 2: You use both HPFS and FAT with                             HPFS active                      FAT passive

If system memory is at least:   Set CACHE: to                  Set DISKCACHE: to                         16 MB         2048                          512 -1024 12 MB        1536                          256 - 512 8 MB        1024                          128 - 256 Set FAT DISKCACHE Parameters: LAZY WRITES                 N/A                               LW

Set HPFS CACHE Parameters: LAZY WRITES               /LAZY:ON                           N/A MAXAGE                >7,500                            N/A DISKIDLE                60,000                            N/A BUFFERIDLE                60,000                            N/A

CASE 3: You use both HPFS and FAT with                             HPFS passive                      FAT active

If system memory is at least:   Set CACHE: to                  Set DISKCACHE: to                         16 MB         1024                             2048 12 MB        768                              1536 8 MB        512                              1024

FAT DISKCACHE Parameters LAZY WRITES                 N/A                               LW

HPFS CACHE Parameters LAZY WRITES               /LAZY:ON                           N/A MAXAGE                >7,500                            N/A DISKIDLE                60,000                            N/A BUFFERIDLE                60,000                            N/A

A few more notes:


 * For purposes of the table above, "active" and "passive" are descriptors for the way a partition is used. If it is seldom used, it is "passive."  If a lot of disk intensive I/O occurs on the partition, it is "active."
 * The HPFS actually requires 128 to 130K of committed memory as opposed to the widely perceived 512K. As cache size increases to 2MB, this requirement increases as well, up to a maximum of about 240K.
 * The optimal cache size seems to be 1536.
 * When comparing the relative merits of the HPFS versus FAT, consider the following: On partitions of identical size, the HPFS gives you about 15% more space and performance is about 28% better!
 * Instead of continuing to increase performance, a DISKCACHE value in excess of 2048 seems to degrade it.

We welcome your comments. Reach us via email on CompuServe userid 71333,2765 or at Proportional Software, 1717 Linden Lake Rd., Ft. Collins, CO 80524, Tel. (800) 666-4672 or (303) 484-2665. Fax. (303) 484-2670.