On Thu, Jun 05, 2008 at 09:16:24PM -0400, Martin K. Petersen wrote: > >>>>> "Jamie" == Jamie Lokier <jamie@xxxxxxxxxxxxx> writes: > > Jamie> Does it handle devices with different properties in differeng > Jamie> offset ranges? E.g. a RAID setup where the first 100GB have > Jamie> one stripe width, but the next 100GB have a different stripe > Jamie> width - as you can get if you join two different hardware RAIDs > Jamie> with LVM, for example. > > 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. So is there going to be any obvious kernel API to access all this info? i.e. if you do an online modification of a volume (e.g. add new storage of a different geometry to the volume) and then do an online grow of the filesystem, how does the filesystem get that new geometry information for the expanded area? FWIW, I don't mind if there isn't a kernel interface for the filesystem to get this information - we're already planning to push complex and dynamic allocation policy configuration out to userspace because it's easier to determine mappings and geometries there.... > 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. > > 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. Most filesystems can't handle existing geometry information, let alone variable geometry. > 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". > > 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... Great ;) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
