Eric Anderson wrote: > Bjoern Koenig wrote: > >> Bjoern Koenig wrote: >> >>> Eric Anderson wrote: >>> >>>> Is it possible to disable all read and write caching to a disk? >>> >>> >>> >>> You can disable write the cache by adding the line >>> >>> hw.ata.wc="0" >> >> >> >> I assumed that you use ATA. If you use SCSI devices then read at least >> the manpages da(4) and camcontrol(8). > > > Thanks.. I've just read (quickly) both man pages. It seems as though > you are suggesting disabling the physical disk caching, which should not > make a difference in my case. The disk would report whatever it needs > to report to either host, and those should be in sync. > > When I mount the filesystem on host B ro, it shows me the filesystem as > of the time that I mounted it ro. Any subsequent changes on host A > (which has it mounted rw) are not seem on host B unless I unmount and > mount again on host B. This seems like a FreeBSD feature and not a > general scsi feature. > > Eric > > > > You simply cannot disable OS caching in FreeBSD. It's a fundamental part of the block I/O and VM layers. There are filesystems like GFS that deal with the issue of directly connecting more than one computer to a disk or set of disks, and there are distributed filesystems like AFS and Coda that deal with making the storage on multiple computers appear as a single network filesystem. Unfortunately, no port of GFS has been done yet, and I estimate that such a port would take 4-6 months. ScottReceived on Thu May 26 2005 - 16:05:35 UTC
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