[Coco] nitros9 proposal - cache sector 0?

[Gene Heskett]

On Saturday 25 January 2014 12:26:29 Aaron Wolfe did opine:

> Interesting to know other drivers have done that, gives me hope there
> is a reasonably safe way.
> I would also not cache writes, that is a bit dicey even for my taste :)
> Thanks for the head up, maybe I can find a one of those drivers and
> take a look at their logic... at least if I implement it and it goes
> all wrong I could sort of blame someone else in that case.
> One wrinkle is that while the DW server knows about disk changes, the
> CoCo itself really doesn't.  Have to think about that one.
> 
> On Sat, Jan 25, 2014 at 11:59 AM, L. Curtis Boyle

One of the reasons its best to cd all shells away from a drivewire image, 
before changing that image, that way the data collected is properly updated 
in the coco drive tables when you cd back to what looks like the same 
location.
> 
> <curtisboyle at sasktel.net> wrote:
> > Some hard drive drivers for OS9/NitrOS9 already cache sector 0 (for
> > reads only), as that rarely changes. Anything with swappable media is
> > a risk for corruption if there is a crash, power loss, etc., which is
> > why it was usually non-removable media that used the cache. Now since
> > Drivewire should be aware when a drive image has changed, you should
> > be able to cache LSN0, and just flag for a forced refresh when the
> > drive image has changed.
> > 
> > Sent from my iPhone
> > 
> >> On Jan 25, 2014, at 10:45 AM, Steve <6809er at srbsoftware.com> wrote:
> >> 
> >> My problem with cache this sector is corruption.  This a very
> >> important bit of information of the file system and should the cache
> >> buffer get damaged by crash code on the CoCo side, you just lost the
> >> disk.
> >> 
> >> A CRC or other check would be needed to verify the data has not been
> >> corrupted.  But the CoCo doing this type of check could take as long
> >> as reading it from the server.  Don't forget that writing this
> >> sector back to the server will take longer because to updating the
> >> cache and the CRC.
> >> 
> >> Good idea, but caching this sector may not save the time that you are
> >> hoping for.
> >> 
> >> Steve
> >> 
> >>> On 1/25/2014 8:05 AM, Aaron Wolfe wrote:
> >>> Its often been noticed that sector 0 of an RBF filesystem gets
> >>> read/written an awful lot when doing nearly any disk I/O.  I've been
> >>> working on the dw server some this morning and am being reminded of
> >>> just how much.
> >>> 
> >>> Would it be practical to cache this sector somewhere?  256 bytes is
> >>> not tiny, but also not impossible to find in the typical system
> >>> page. The logic for a simple write-through cache would not be very
> >>> complex.
> >>> 
> >>>  I guess I'm looking to the experts for reasons this can't work or
> >>> 
> >>> should never be done before looking at how to do it :)  Any
> >>> thoughts?
> >>> 
> >>> -Aaron
> >>> 
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Cheers, Gene
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