Messages in this thread |  | | From | Rob Landley <> | Subject | Re: Poor floppy performance in kernel 2.4.10 | Date | Sat, 20 Oct 2001 00:20:38 -0400 |
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On Friday 19 October 2001 11:57, Linus Torvalds wrote:
> Well, the original reason to not trust the media-change signal is that > some floppy drives simply do not implement the signal at all. Don't ask > me why. So a loong time ago Linux had the problem that when you changed > floppies you wouldn't see the new information - or you'd see _partially_ > new and old information depending on what your access patterns were and > what the caches contained. > > So it's pretty much across the board - broken SCSI, broken floppies, > just about any changeable media tends to have _some_ bad cases. And with > the floppy case, there was no way to notice at run-time whether the unit > was broken or not - the floppy drives have no ID's to blacklist etc. So > either you tell people to flush their caches by hand (which we did), or > you just always flush it between separate opens (which we later did). > > Linus
The original dos case was timeout based. They sat down and changed the disk as fast as they could, and worked out it took something like two and a half seconds to swap disks. So if subsequent accesses were within two and a half seconds and got valid data on the first attempt, they decided it had to be the same disk...
These days with the button it's probably more like a second and a half, but the principle's the same.
Also, enough drives do it right (the vast majority), that a "broken_disk_change" module/boot option seems more sensible as a non-default thing for those that really are hosed...
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