harrow@exodus.dec.com (Jeff Harrow, NCSE LKG1-3/F16 DTN=226-7445) (10/17/86)
I believe that we have finally put to rest the confusion about the Mac-Plus Control Panel Cache: It is **NOT** write-thru. Hence you **DO** risk that in a crash situation, files which you THOUGHT were safe (you SAVEd them) can really be left in an un-updated, or even corrupt state. I still don't understand why Apple would choose this dangerous type oc cache when the Mac usually defaults to the safest mode (yes, non-write thru IS faster, but so is not asking a user if he wants to save a modified document when he quits the application...). Now for my question: Since Apple didn't even offer the OPTION of choosing safety over speed (a radio button to show a DEFAULT of write-thru, with the OPTION of non-write-thru), has anyone figured out a SAFE patch to the cache code to make this non-write-thru cache into a write-thru one? Jeff Harrow
dgold@apple.UUCP (David Goldsmith) (10/18/86)
In article <6009@decwrl.DEC.COM> harrow@exodus.dec.com (Jeff Harrow, NCSE LKG1-3/F16 DTN=226-7445) writes: >I believe that we have finally put to rest the confusion about the >Mac-Plus Control Panel Cache: It is **NOT** write-thru. Hence you **DO** >risk that in a crash situation, files which you THOUGHT were safe (you >SAVEd them) can really be left in an un-updated, or even corrupt state. > Although this has been discussed on the network before, I'll try to clarify the situation. Although it IS true that the Mac Plus cache is not write-through, it is NOT true that files you thought you saved may be corrupted. After completing any operation such as a save, application are supposed to call the File Manager routine FlushVol. This updates the volume directory and FLUSHES THE CACHE. The requirement that applications call FlushVol after Save and similar operations is not a new one; it has been present since day one and for MFS as well as HFS volumes. Even before there was a Control Panel cache there were volume directory caches which needed to be flushed by FlushVol. To summarize, if your application is written correctly (i.e., calls FlushVol at the appropriate times), your data is safe whether the cache is on or not. If it doesn't call FlushVol correctly, your data may not be safe, whether the cache is on or not. I've been using the cache for about a year now and have never lost any data because of it, despite some pretty spectacular crashes. David Goldsmith Apple Computer, Inc. Development Systems Group UUCP: {nsc,dual,sun,voder,ucbvax!mtxinu}!apple!dgold CSNET: dgold@apple.CSNET, dgold%apple@CSNET-RELAY