On Wed, Feb 29, 2012 at 4:23 PM, Douglas Gilbert <dgilbert@xxxxxxxxxxxx> wrote: > On 12-02-29 06:27 PM, Dan Williams wrote: >> >> On Wed, Feb 29, 2012 at 2:40 PM, Douglas Gilbert<dgilbert@xxxxxxxxxxxx> >> wrote: >>> >>> On 12-02-29 04:55 PM, James Bottomley wrote: >>>> >>>> >>>> On Fri, 2012-02-10 at 00:45 -0800, Dan Williams wrote: >>>>> >>>>> >>>>> It is possible for a host to get "locked out" from talking to sata >>>>> devices in the domain if, for example, its sas address changes but the >>>>> expander topology has existing affiliations with the old address. If >>>>> the system is booted userspace can write to >>>>> /sys/class/sas_phy/<phy-X>/hard_reset to clear the affiliation, however >>>>> if this condition exists for the root device the module parameter can >>>>> be >>>>> used to promote all ata resets to hard resets. >>> >>> >>> >>> A point of order: SAS has link resets and hard resets. The >>> hard reset is a superset of link reset. A "link reset sequence >>> serves as a hard reset for SATA devices" and hence is >>> sufficient to reset a SATA device. To reset a SAS device >>> (e.g. a SAS disk) you need a SAS hard reset. Therefore a link >>> reset is the appropriately sized "gun" to reset a SATA device. >>> >>> I have a SAS-2 expander that annoyingly powers up with the >>> programmed maximum physical link rate of its phys at 3 Gbps >>> even though its hardware maximum rate is 6 Gbps. For expander >>> phys connected to SAS-2 disks I can up the programmed maximum >>> value to 6 Gbps on the expander phy then do a link reset on >>> that phy. So without upsetting Linux (or any other OS) I can >>> switch that path from 3 Gbps to 6 Gbps. Can't do that with a >>> SATA disk without the OS finding out. >> >> >> At least now (with these pending patches) if you trigger a link-reset >> via the sysfs interface libsas will manage the link recovery like any >> other error-recovery initiated reset. > > > I can think of 4 cases for link reset. The other end > of the link is: > a) a SAS target: not error recovery situation > b) a SAS expander phy: not error recovery situation > c) a SATA device: error recovery situation sas_try_ata_reset() [1] is what promotes user requested resets into error recovery managed resets if the other end of the link is sata. [1]: http://git.kernel.org/?p=linux/kernel/git/djbw/isci.git;a=blob;f=drivers/scsi/libsas/sas_init.c;h=57e7ac97b3e3dba3091f83a64c0c32a6660390cb;hb=refs/heads/all#l222 -- 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
