Independant AFS FAQ - Common Questions

AFS FAQ
Common Questions
Last updated 23-February-1997

Copyright © 1996-1997 Mark Harden - All rights reserved.
Please do not copy. Make a link. That way we have one up to date copy !
E-Mail : faq@harden.demon.co.uk

Table of contents - Common Questions

How does AFS work ?
Does AFS have a cache ?
What does AFS use its buffers for ?
How do I undelete a file ?
What is a RollOver log file ?
Will AFS work with removable media like Zip and SyQuest drives ?
Is there any software that I may have problems with ?
Does DiskSalv understand AFS ?
Does ReOrg understand AFS ?
Does AFS work with disk compressors ?
Can I use a disk cache with AFS ?
Can I use GigaMem or VMM with AFS.
What is disk fragmentation ?
How can I tell if my partition is fragmented ?
How do I defragment my partition ?

How does AFS work ?

AFS grew out of PFS. If you are interested in how it works look for PFS on AmiNet :-

    pfs95.lha   disk/misc  232K  Professional file system for the Amiga

In an interesting turn of events Michiel Pelt, the author of AFS, posted the AFS diskstructures to the AFS mailing list. To read this message follow this link...

This information can be used to manually repair an AFS partition.

Does AFS have a cache ?

Yes and no. AFS caches it's reserved area. This contains all directories and information required to access files. AFS does not cache the contents of any file. The exception of this is small reads and writes that are cached for a while.

What does AFS use its buffers for ?

AFS Uses it's buffers to cache its reserved area and to buffer small reads and writes.

How do I undelete a file ?

AFS remembers the details of the last 31 files deleted. If it is possible to undelete the file it will be placed in the :.deldir directory. Note that to guarantee uniqueness a slot number is appended to the filename.

To undelete a file simply copy it from the :.deldir directory and correct the protection bits. It is a BAD idea to copy the file to the same partition as this may use the space of the file you are recovering which WILL result in a corrupt file.

Note that you cannot rename files from the :.deldir directory.

Guy Baltet has written a program to automate this process with a nice MUI GUI interface. It is available from AmiNet :-

    disk/misc/AFSUndelete1.5.lha

Please do not ask FLD for support for this program.

What is a RollOver logfile ?

Under the normal system every time you add an entry to a logfile, it is appended to the end of a file, and the file gets bigger. This causes 2 major problems :-

You have to shorten or delete the logfile every so often.
The logfile gets very fragmented.

Using a program call 'MakeRollOver' you can create a new logfile. When it is created you should choose how many disks blocks you wish to allocate to the logfile. This space is allocated immediately although the size will show as 0. As data is appended to the file it will grow in size until it reaches the size you allocated. After this point data will still be appended to the end of logfile, but the file will not get any bigger. This is achieved by AFS removing the oldest entries from the start of the file.

Note that when you create a RollOver file you specify the number of blocks to allocate. Not the number of bytes !

Note also that RollOver files are converted to normal files by all known backup systems. If you ever have to restore you will have to rename the file, create the RollOver version and copy the data back into it. Remember to delete the temporary copy !

Will AFS work with removable media like Zip and SyQuest drives ?

Yes. The User version will work, too, as long as those drives are the only one AFS is on and the drives have a capacity of less than 650MB (which is the case for all current models). Fourth Level Development has special removable media support tools which they bundle with drives. These packages are now available seperately. Without this software, you have to do the same thing you would with FFS on removable media -- HDToolbox, etc.

It is suggested that you partition all your cartridges the same. The Amiga reads the RDB, partition table, at boot time only. You should also leave a disk in the drive when you boot.

FLD's software is call Momiga Tools and costs UK£ 49.95 + 2.50 P&P.

Is there any software that I may have problems with ?

Most software works fine with AFS. As with any changes to the system (such as an upgrade from 1.3 to 2.0, or 2.0 to 3.1, or running a graphics card, etc.), there can be compatibility problems with some very small number of titles. Here is the list of problems Fourth Level has heard of, with notes on what is being done to address the problems. Note that most are expected to be fixed !

    DiskExpander  - Does not work with AFS (Author checking).
    Dopus5        - Does not register with AFS (Patch on AmiNet).
    Excelsior BBS - Some functions do not work under AFS (Author checking)
    Diskspare     - Does not work with muFS and AFS at the same time.
    Virocop       - Does not work with AFS (Author checking).

Note that some HD Prep tools do not support custom filesystems, in general, the best thing to do is use rdbprep (On AmiNet) instead.

    DOpusReg.lha  biz/dopus    3K  Opus 5.11 fix for AFS pro
    rdp391.lha    disk/misc  136K  HD prep utility from MicroBotics

Does DiskSalv understand AFS ?

Yes and no. DiskSalv4 understands AFS but only in SALVAGE mode. Some users wanted some form of "security" so FLD released an early version. This was to be upgraded free to the full version when available. This will NEVER happen. There is alreay a more recent version but FLD's customers cannot upgrade. For more details please read about the Valentines Day offers.

FLD can no longer supply DiskSalv4 or any upgrades. In the US you can get it from IAM :-

   DiskSalv4                US$40
   Upgrade from DiskSalv3   US$10

Postage will be extra. Please email IAM for further details.

Note that DiskSalv4 will NOT understand AFS V3.0 and above.

Does ReOrg understand AFS ?

No.

At the moment ReOrgAFS is on hold. It currently seems very unlikely that it will ever be finished and released.

Further details are not available at this time, but that any changes will be announced on the AFS mailing list.

There are some ways to minimise <#015>fragmentation.

FLD made an unauthorised announcement that I was working on a DeFrag tool for AFS.

Does AFS work with disk compressors ?

DiskExpander is NOT OS legal and will therefore NOT work with AFS.

XPK Works fine.

Can I use a disk cache with AFS ?

Yes with care.

AFS caches its reserved area in it's buffers. You should ensure that you have enough buffers for this.

AFS is a secure filesystem. The order that data is written to the disk is critical. If you use a cache do NOT enable ANY write caching.

Note the 2.4 includes some caching.

Can I use GigaMem or VMM with AFS.

Yes. Page files and partitions all work fine. VMM pseudo-partitions do not work. This is because VMM understands the FFS disk layout and not that used by AFS.

Note that virtual memory managers work best to their own partitions.

What is disk fragmentation ?

When a file is written to disk a block is allocated. As more and more is written to the file other blocks will be allocated. Ideally all the blocks of the file would be next to each other in one large chunk. This means that when the file is read the disk head doesn't have to move. It can "scoop" up the file in one go.

Fragmentation occurs when the allocated blocks are scattered across the disk.

One of the speed benefits come from the fact that AFS maps a file with a-nodes. This carries the details of one chunk or fragment. Ideally a file will be mapped by one a-node. When you "seek" into a file AFS can do this quickly. FFS has to look at the file header and extension blocks.

How can I tell if my partition is fragmented ?

First you need the unit name. Type "info" and find the partition of interest. Read the partition name from the first column. Now type :-

   DiskValid Analyse <unit>:

This will list all fragmented files.

Do not panic if a number of files is found. You should worry if a number of files has more that 8 fragments.

How do I defragment my partition ?

In an ideal world you would run ReOrgAFS. As stated earlier there is no such program.

The biggest source of fragmentation is appending data to existing files. Log files are prime cases of this. You should make use of RollOver log files where possible.

The only way to defragment files is to copy them. The only other way is to backup the partition and restore it. Note that RollOver log files are restored as normal files and should be converted back afterwards !

Martin Steigerwald has written a program for doing this. It is available from AmiNet or FLD's FTP server :-

    aminet: disk/optim/afsdefragtry.lha
    ftp:    ftp.flevel.co.uk:/pub/afs/contrib/afsdefragtry.lha

Please do not ask FLD for support on this program.