On 07/16/2009 08:22 PM, david@xxxxxxx wrote: > On Thu, 16 Jul 2009, Boaz Harrosh wrote: > >> On 07/16/2009 04:09 AM, david@xxxxxxx wrote: >>> is there any way to get deterministic device ordering with scsi async >>> scanning? >>> >>> currently (2.6.30) it seems that the various scsi busses are loaded in the >>> order that they are detected, which can vary from boot to boot depending >>> on how long it takes for the card to initialize. >>> >>> would it be possible to detect the cards/drives, but not register them >>> until all the detection is complete so that they can be registered in a >>> deterministic order? >>> >>> having two drives on two different controllers swap positions from boot to >>> boot makes it very painful. yes I can make an initrd that fixes this up in >>> user space by examining each drive and creating links to re-order them, >>> but this is a lot of work to fix randomization that can be prevented in >>> the first place. >>> >>> David Lang >> It is highly discouraged to setup any kind of system that depends >> on device-names for block-devices. mounts have the mount by-label >> or mount by-uuid. Any other subsystem should go by /dev/disk/by-id/* >> slinks to find a persistent raw block-device. the id is generated >> from characteristics inside the disk itself so it will be the same >> no matter what host connection or bus it is connected too (almost). >> >> This is because even if the boot order is consistent, the device-name >> is so volatile in the life-span of a system. Did I boot with a removable >> USB inserted. that camera or printer was on or off, disk was connected >> to the other port. Any such change will break things and give you a very >> poor user experience. > > for a laptop you areprobably correct, but for a server or embedded system > that doesn't have it's hardware changing all the time you are not correct. > > especially on a system with lots of drives, why should I have to create an > initrd that goes and searches dozens or hundreds of drives to find out > which one to boot from? > there is *no* searching with /dev/disk/by-id/ or /dev/disk/by-uuid/ Udev comes reads a small piece of information and puts up a link. now: not(initrd+Udev) == Kernel_with_no_legs > I am building a system that will have two drives in a hardware mirror on > one SCSI card, and 160 drives on a FC (SCSI) card. why should my boot have > to go and examine all 162 drives to look for an ID on every partition just > to find the boot drive? > Again no searching is done here, just read of a sector for uuid and some query command for by-id >> I would say that "scsi async" is a grate blessing > > it's great for startup time, but doing the async detection doesn't > _require_ doing async registration. > > David Lang Boaz -- 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
