Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!nrl-cmf!ames!oliveb!amiga!cbmvax!steveb
From: steveb@cbmvax.UUCP (Steve Beats)
Newsgroups: comp.sys.amiga
Subject: Re: UnDelete & DiskSalv Question
Message-ID: <3337@cbmvax.UUCP>
Date: 18 Feb 88 14:26:10 GMT
References: <18956@aspvax.UUCP> <41962@sun.uucp> <3325@cbmvax.UUCP> <2908@swan.ulowell.edu> <42225@sun.uucp>
Reply-To: steveb@cbmvax.UUCP (Steve Beats)
Organization: Commodore Technology, West Chester, PA
Lines: 35

In article <42225@sun.uucp> cmcmanis@sun.UUCP (Chuck McManis) writes:
>In article <2908@swan.ulowell.edu> page@swan.ulowell.edu (Bob Page) writes:
>>steveb@cbmvax.UUCP (Steve Beats) wrote:
>>>If the file was closer to the root than the current bitmap then the
>>>chances are it will be zonked
>>
>>This isn't an issue on floppies, where the bitmap gets allocated at
>>format & doesn't get deallocated, since there's only one.  
>
>Uh Bob, if you look at where your floppy bitmap is on your floppy you
>might be suprised to see that it moves around.  ............
>.......Steve, does it still move on FFS systems?
>
No way, Jose!  FFS allocates the bitmap as soon as it can (ie when the disk
has just been formatted), and leaves it there permanently.  There is one
possibly nasty side effect from this though.  If the bitmap gets allocated
in a really wierd place or is fragged up a lot then it will remain that way.
I can't think of any case where this could happen with the current FFS
because you can't write to a disk that is validating (and hence can't steal
blocks from the bitmaps preferred area).  But, when FFS gets updated (soon) and
supports old FS format, there could be some gotchas.  Imagine a floppy that
is 100% data, no bitmap block allocated.  This is perfectly legal as you
pointed out Chuck since the validator will construct a bitmap in memory. As
soon as you delete a file from this disk, the bitmap will use whichever key
becomes available first.  If this is off to the edge of the disk, than that
is where it will stay.  I made the decision that since the bitmap is only
accessed during startup and the 3 second update, the performance hit would
be acceptable.  Wanna hear a horrible fix?  Delete a file that is known to
be close to the root and reboot the machine after it has finished but before
the 3 sec write has occured.  On re-boot, the validator will construct a new
bitmap and allocate it in the space left by the deleted file.  Of course,
this would only be an issue on floppies that were created using oldFS and
were subsequently used with the compatible version of FFS.  

	Steve