Martin K. Petersen wrote: > I touched on this in my reply to Andreas. The values exported in > sysfs are only part of the solution. We'll still need some > intelligence (in libdisk or elsewhere) to traverse the stacked device. > And that's better done in user land where it's easier to notify the > operator or ask for confirmation. Agree, except for one thing. It would be good to able to get a consistent atomic snapshot of the whole stack in one kernel call. I guess that's not feasible where network devices are involved, though, without a rather complicated interface. > Jamie> If it's a set of drives, doesn't it need to return multiple > Jamie> offsets, and drive identities? > > Given the almost infinite amount of stacking and concatenation options > I think we'll quickly get into FIEMAP territory. Add snapshots to the > mix and mapping out the characteristics quickly becomes unmanageable. Well, not unmanagable, but large and unsuitable for many programs. > If we present the mkfs writers with a list of 200 regions with > different alignment criteria and stripe sizes I'm sure they'll get > very unhappy. Probably right. But as a database writer, I'd like the information if I can get it. Sometimes I'll do timing measurements, because they are more "real" than the kernel's estimate. But I can't measure storage stability levels, that really needs data from the kernel (if the kernel even has it). > So instead of publishing all this information I'd much rather have > libdisk do a rudimentary check and make it a binary "looks good" > vs. "may have performance problems". Sensible, I agree. > If some poor mkfs souls wantsto traverse the entire stack and actually > make the filesystem layout completely heterogeneous, my patch also > allows them to do that... Good, being possible is the main thing :-) And preferably without a different interface for different kinds of device. So as long as there's a way to traverse the stack generically. -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
