On Thu, Dec 17 2015, Dan Williams wrote: > On Tue, Dec 15, 2015 at 6:01 PM, NeilBrown <neilb@xxxxxxxx> wrote: >> On Wed, Dec 02 2015, Song Liu wrote: >> >>> These patches by Dan Williams enable creating RAID array based on >>> SCSI enclosures. >> >> Is there any background reading available so I can have some idea what >> these patches are supposed to do. > > "Blink the light when the disk dies", is the terse summary. > >> I have a vague idea what an "enclosure" is but I didn't know that Linux >> knew about them. Is there a link to the LWN article about them or some >> other useful documentation? "git grep -i enclosur Documentation/" >> didn't show anything likely to be useful. > > The interface these patches use is presented by the "ses" driver > (drivers/scsi/ses.c) which leverages the sysfs interface presented by > the "enclosure" driver (drivers/misc/enclosure.c). I don't recall > their being much in the way of documentation. > > For each disk in an enclosure the driver exposes an enclosure object > with the following attributes: > fault > status > active > locate > power_status > type > slot > > Where 'fault', 'active', and 'locate' select different led signal > patterns. The 'power_status' attribute allows power to be turned off > to the slot. The 'slot' attribute is meant to match the slot > identifier that is on the board's silk screen or some physical label a > technician can observe. cat > Documentation/scsi/ses.txt ??? Thanks. That is useful background. > >> And what is "/dev/disk/by-slot"?? I've never come across it before >> and google doesn't help much. Just these patches and >> http://comments.gmane.org/gmane.linux.scsi/93809 > > /dev/disk/by-slot are new proposed symlinks for udev. The new udev > rules for this are in patch1. If this is proposed, then there must be a proposal - right? Written?? (I doubt it). So "by-path" is about the data-path that leads to the device, but "by-slot" is about the physical location of the device (which may correlate with the path, but is conceptually different). I guess I can accept that. I don't suppose "by-location" was considered? Can a "disk" have other locations that "slots"? I guess 'sd' cards live in slots. But USB sticks plug into sockets (or are sockets just slots?) CDROMs live in trays. Is there some convention for naming slots? enclosure-rank-row-column ?? Is there some convention for naming enclosures? Bob, Jane, Ahmed? > > When the scsi core is probing devices and finds an enclosure target > device it associates enclosure slot objects with the scsi_target. > With that association we can create a symlink for the resulting disk > based on its physical slot identifier. > > At the time mdadm was chosen to house these rules for convenience, but > I think they should be submitted to upstream udev. Yes, I would definitely like to see this "by-location" ;-) proposal accepted by upstream udev before committing to it in mdadm. Thanks, NeilBrown
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