Path: utzoo!mnetor!uunet!portal!atari!apratt
From: apratt@atari.UUCP (Allan Pratt)
Newsgroups: comp.sys.atari.st
Subject: Re: Turbodos and the ideal disk cache
Message-ID: <1052@atari.UUCP>
Date: 4 May 88 17:51:33 GMT
References: <307@zinn.MV.COM>
Organization: Atari Corp., Sunnyvale CA
Lines: 34

From article <307@zinn.MV.COM>, by mem@zinn.MV.COM (Mark E. Mallett):
> well, there's another answer somewhere between write-through and write-back
> cache, and that is the idea of having some control over when updates are
> posted to disk.
>
> [Important stuff deleted; go read the original article if you care.]

Please!  GEMDOS is not so foolish as to write to the disk every time a
cluster is added to a file.  Buffers in the cache are ALWAYS tagged
in the "mark as dirty" mode when written to.  Then, if the operation
doing the writing wants it updated immediately, it says so.

However, GEMDOS always flushes its whole cache when you close a file.
This is to update the FATs, directory, and any data sectors in the cache.
Also, when you do most directory operations (rename, create, delete)
the directory sector is written immediately.

This introduces inefficiency when you are (for example) deleting a bunch
of files.  Rather than write the FAT and directory sectors after each
delete, a delayed-write cache could do the whole sequence of deletes in
RAM, and write them only once.  The trouble, as I mentioned in my
original posting, is that you can't tell when a series of deletes is
finished.

Delayed writes are hazardous to your disks, and especially to
your floppies.

Can anybody tell me categorically that TurboDOS does or does not delay
writes? For instance, can you give me a recipie for demonstrating and
reproducing the delayed-write phenomenon?

============================================
Opinions expressed above do not necessarily	-- Allan Pratt, Atari Corp.
reflect those of Atari Corp. or anyone else.	  ...ames!atari!apratt