Messages in this thread | | | Date | Wed, 02 Apr 2008 22:21:13 -0600 | From | Robert Hancock <> | Subject | Re: Slow tape drive timeout |
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Kai Makisara wrote: > On Tue, 1 Apr 2008, Carlo Nyto wrote: > >> I am experiencing a two minute timeout open()ing a tape device when >> there is no tape in the drive. >> >> open() with O_NONBLOCK succeeds immediately, however. >> > This is how open() is supposed to work according to standards (e.g., SUS) > if O_NONBLOCK is supported. (Well, actually open() should wait > indefinitely but the non-linux systems I tested had a timeout.) The linux > st driver was changed to comply with standards at 2.5.3. I.e., the 2.4 > kernels did return immediately but the 2.6 kernels have always waited. > >> The problem is that I am trying to set up Legato on a system that has >> multiple tape drives. For certain common operations, Legato tries to >> open() each tape drive multiple times. On a system with multiple tape >> drives, this adds up to a significant amount of time wasted due to >> this timeout. >> > You are not the only person who has noticed this. At work we had to > install a distribution using 2.4 kernel to our backup server in order to > use Legato ;-( > > But this is a Legato problem, not a kernel problem. > >> Solaris does not have this problem, and Legato support advises that >> they are at the mercy of the operating system. >> > Solaris does return EIO. Either it does not support O_NONBLOCK or it is > not compliant with SUS. > > Legato would not be so much "at the mercy of the operating system" if they > would write their software to work according to standards, not according > to some operating system.
Why is accessing the tape drive with no tape in it causing a timeout in the first place? I should think that would fail immediately with some "medium not present" error from the drive. Unless the drive has no mechanism to detect it, but that seems really retarded..
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