On 12/3/2012 1:15 AM, Hannes Reinecke wrote: > Well, looking at QLogic and Emulex both emulate a bus reset with a loop > over each target and invoke a target reset there. I somewhat fail to see > the rationale behind it, other than emulating the bus reset behaviour on > SPI. It is actually a _VERY_ bad idea in multiple initiator tape environments with switched fibre where the resets can affect devices that are visible but not owned/controlled by the machine broadcasting resets. Many tape environments operate this way as the physical drives are assigned dynamically to initiators as necessary. In some cases (ACSLS) the machine/OS/backup applications aren't even homogenous. The rewind and loss of PR/etc, which if not handled properly by all the other machines on the SAN can be quite disastrous. Its also somewhat problematic even in single initiator environments as the reset can affect devices not having problems, and the 6/2900's can get eaten by the logic attempting the reset, which leaves the user of a functional device in the dark that it was reset/rewound. I was told last time I brought this up, that it was impossible for a single device's failure to result in that bus reset path being called. Which was patently false as the problem was only tracked down because of a repeatable case of a single device failing in a manner which triggered progressively more aggressive recovery culminating in the bus-reset being called. The result was a single device cascading a failure to a bunch of functional devices and interrupting their operation. -- 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
