AWCTTYPA@UIAMVS.BITNET ("David A. Lyons") (02/04/89)
>Date: Wed, 1 Feb 89 22:53:06 GMT >From: Doug Gwyn <haven!adm!smoke!gwyn@AMES.ARC.NASA.GOV> >Subject: Re: GS/OS Cache (was Re: RE: Re: Bad //gs?) >>GS/OS maintains a cache regardless of the setting in the Cache DA. This >>is one of the reasons for its efficiency compared to ProDOS. > >Not a write cache, as I have heard it explained. If it DOES fail to >"write through" the cache and it gets its cache scrambled when it >aborts out of a folder copy operation, that could explain why the >disk ends up corrupted. With the cache size set to 0, there is still a 16K cache. I don't believe there's anything special about that remaining 16K--it's just that the system won't let the cache go away completely, because of the large difference it makes in efficiency. What is a "write cache"? The cache is normally "write-through," meaning that anything written to the cache is _also_ written to disk at the same time. The only time it will "fail" to write-through to disk is when a SESSION is in progress. Sessions are a way for an application to _intentionally_ suspend the write-through nature of the cache while, say, many files are copied at once. When the session ends, all the cached blocks that haven't been written to disk are written (in an efficient order, too). Volume-full situations should not present any special problems, since the session only affects when the blocks are written to your _disk_: it doesn't affect the contents of your _volume_ from the point of view of any higher-level part of the system (File System Translators, GS/OS itself, or the application [Finder or whatever]). The only thing the Finder needs to worry about is always calling END_SESSION when it should. I _tried_ to duplicate the problem you described, and I haven't been able to. Can you describe the circumstances in more detail for me? --cache size setting --total RAM in system; free RAM in system --volume size (can you do this on an 800K disk?) --free space on volume --size of folder being duplicated, and sizes of the items inside the folder --David A. Lyons bitnet: awcttypa@uiamvs DAL Systems CompuServe: 72177,3233 P.O. Box 287 GEnie mail: D.LYONS2 North Liberty, IA 52317 AppleLinkPE: Dave Lyons
gwyn@smoke.BRL.MIL (Doug Gwyn ) (02/05/89)
In article <8902032353.aa26938@SMOKE.BRL.MIL> AWCTTYPA@UIAMVS.BITNET ("David A. Lyons") writes: >--cache size setting 0 >--total RAM in system; free RAM in system 2.25Mbytes, 2.25Mbytes - GS/OS - Finder (i.e. RAM disk size 0) >--volume size (can you do this on an 800K disk?) 20Mbytes (HD20SC, Apple II SCSI card) >--free space on volume Approx. 1Mbytes >--size of folder being duplicated, and sizes of the items inside > the folder Approx. 1.5 Mbytes, items of variable sizes from one block on up, including several subdirectories a couple of levels deep.