Messages in this thread | | | Date | Thu, 16 Jul 2009 10:22:34 -0700 (PDT) | From | david@lang ... | Subject | Re: deterministic scsi order with async scan |
| |
On Thu, 16 Jul 2009, Boaz Harrosh wrote:
> On 07/16/2009 04:09 AM, david@lang.hm 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?
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?
> 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
| |