Stefan Richter wrote: > James Bottomley wrote: > >>Assuming the cages are all powered up, which is beyond >>the driver control, then serialising the scan will allow one to >>specify /dev/sda1 deterministically for root. > > > Does SAS provide a persistent globally unique property of a device, or > has SAS to rely on bus topology to uniqely identify devices? That swings on what you mean by "device" but broadly: Yes to the first part, but ... SAS is a transport and SAS transport endpoints (i.e. "ports") have naa-5 world wide unique identifiers. That might sound great but most SAS disks are dual ported, so that gives two SAS (i.e. naa-5) addresses (typically consecutive). A dual ported SAS disk could/should have up to 4 naa-5 addresses: - one for SAS port 1 (primary) - one for SAS port 2 (secondary) - one for the target device - and, one for the logical unit A SAS (target) device might also be a bridge, for example, as found in SAS expanders that support SATA devices. SATA disks do not yet have mandated world wide unique addresses (but provision has been made for a naa-5 address). The SAS "port" address of a SATA disk is actually the bridge it is plugged into (but one could switch SATA disks). I suspect what you would really like to identify uniquely is the logical unit. Fuzziness remains due to the possibility of bridges. Doug Gilbert - : 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
