• Is there a minimum or maximum partition size ?
• What block sizes does AFS support ?
• What is MaxTransfer ?
• What value should MaxTransfer be ?
• What is DMAMask ?
• What value should DMAMask be ?
• How many buffers should I assign to each AFS partition ?
• How do I change the number of buffers used by a partition ?
• Do I have to reformat my partition to use AFS ?
• What is direct SCSI support ?
• Should I use the direct SCSI version ?
• Can I run more than one version of AFS ?

Version 2.4 breaks the 4GB drive limit by using direct SCSI commands.

CD-ROM uses 4096 byte blocks so AFS cannot be used on them.

By the way, the MaxTransfer value is hardly important for the disk performance - a value of 0xFFFFFF means "16MB maximum in one transfer" while a value of 0xFFFF is still 64K. I once set it as low as 2K and the loss of speed was hardly noticeable.

IDE Drives  - Try 0x1FE00.  If files greater than 64K get corrupted
                            then reduce it to 0xFE00.

SCSI Drives - Use 0xFFFE00.

Please test your set up by copying large files and testing that they were copied correctly. I have heard of a SCSI disk on an A2091 card that would only work with small values. If in doubt use 0xFE00.

I will not give "optimal" values here. These values will get you going. If you want every once of speed you can increase the value until you get errors and the drop to the previous value. Use powers of 2 less the size of a block (512). Any speed increase will be VERY small and possibly not worth the risk.

1. High speed devices like disk controllers can read data straight from memory without any CPU load. This access is call direct memory access or DMA.

   Standard Amiga devices can only use CHIP memory for DMA. Disk controllers are usually capable of using DMA to any memory.

   The DMAMask value restricts DMA activity by a particular device driver to a particular area of memory.

   The default value of 0xFFFFFF restricts DMA to the ZorroII area. This is a bad idea for any ZorroIII based machine which always has memory outside this area. In this case 0xFFFFFFFF would be a better value.

2. The DMAMask also control the alignment of any buffers used to access the device. The least significant bits are used to control this. Values with no zero bits, end in 0xF, will have no alignment. Values with one zero bit, end in 0xE, will be word aligned. Values with two zero bits, end in 0xC, will be long word aligned.

   The alignment can make a lot of difference to performance. Longword alignment is usually the best.

Read the instructions that came with your computer or disk controller. Can it access all memory on your machine ?

If this doesn't help look at your memory map with ShowConfig. Use the maximum memory address as a starting point and adapt it as follows :-

1. The DMAMask should start with 1, 3, 7 or F. If not substitute the higher value in the list.
2. Substitute all other digits with F.
3. Change the last F to a C.
4. Use this value.

The following table gives some examples :-

      Address  |   DMAMask
   ------------+---------
    0x001FFFFF | 0x001FFFFC
    0x005FFFFF | 0x007FFFFC
    0x07FCFFFF | 0x07FFFFFC
    0x07FFFFFF | 0x07FFFFFC

If you add memory to you machine you should review you DMAMask settings BEFORE you install the memory ! Another, poorer, option is to set the DMAMask to 0xFFFFFFFC from the word go. This is option is NOT available if your disk controller needs a specific type of memory. See 70.

    100 - Minimum
    150 - Normal partitions
    250 - Large directories (>2000 files)

Remember that each buffer is 1024 bytes and NOT 512 as is true for FFS.

AFS 2.2 (15.9) sanity checks the number of buffers ensuring that the value is between 50 and 300.

AFS 2.4 (16.16) sanity checks the number of buffers ensuring that the value is between 70 and 500.

• How many buffers should I assign to each AFS partition ?
• How do I change the number of buffers used by a partition ?

1. Use HDToolBox
2. Use AddBuffers in you S:User-StartUp

You can also check the number of buffers with AddBuffers.

• Scan the disk noting directory information
• Move any files out of the AFS reserved area (directory area)
• Create AFS reserved area
• Change RDB and root block

Most SCSI and IDE device drivers support this option.

Note that there is no speed benefit to using the direct SCSI version on IDE drives.

If you have a SCSI disk then try it out !

A number of people have reported problems with the direct SCSI version. If you do not need it I suggest you avoid it.

Before you attempt this you should ensure that your RDB is large enough to hold two versions of AFS. See question 33.

You should follow the instructions for installing AFS as given in the manual except that instead of specifying the ID 0x41465301 you should use 0x41465309. For each partition you want to use the new version you should go to the partition window in HDToolBox. Select advanced options and then select change. Clock on the file system button at the top until AFS\09 appears. Select OK. Select OK. Save changes to drive. You will get a warning about trashing the data. HDToolBox assumes that you are installing a new file system. You are not. It is safe to ignore this warning. You will have to reboot for changes to take effect !

When you are happy upgrade AFS as instructed in question 59 and deleted the second copy with the ID 0x41465309 from the file system window.