On Nov 5, 2018, at 12:10 AM, Ulrich Windl <ulrich.wi...@rz.uni-regensburg.de> wrote: > > Hi! > > I wonder: On Fibre-Channel (FC) SAN stroage systems, some systems indicate > when there are new LUNs available, while others do not. Linux clients > sometimes understand what the storage system is telling them, sometimes not. > So usually one has to rescan the scsi bus to find new (or obsolete) LUNs. > Does the SCSI protocol have provisions to indicate a new target is available? > Maybe it depends on the details: I'd guess a device that is in the state of > becoming ready would be detected, but would have a state like "target is > becoming ready" (which could be polled using TUR, I guess). > If the whole storage system is down, the situation is different, but in the > FC case a new target would be still signalled on the FC bus at least (via LIP > (loop Initialization Primitive) I think)... > > Could such events trigger an iSCSI login? > > Regards, > Ulrich
Fibre Channel has asynchronous notification built into its protocol (as does InfiniBand), since those standards were created *after* SCSI was well established. There is a thing called AN (asynchronous notification), but it’s thinly supported and not available at all for storage systems. Yes, of course a client can poll a storage box, but iSCSI in general does not do this, as part of its protocol. The best solution for iSCSI, IMHO, is ISNS. That is what iSNS was designed for. If you’re using targetcli-fb as your iSCSI target, it supports iSNS, as does open-iscsi. Part of the reason for this lack of support is that SCSI was designed for static discs, i.e. it was not expected that discs would be coming and going all the time. A disc is just supposed to be there, all the time (like dial tone). So the SCSI protocol assumed that was the case. If you want truly asynchronous storage, but a commercial FC storage box (IMHO). If you want asynchronous iSCSI, use iSNS (see open-isns, a project I maintain on github). — Lee Duncan -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to open-iscsi+unsubscr...@googlegroups.com. To post to this group, send email to open-iscsi@googlegroups.com. Visit this group at https://groups.google.com/group/open-iscsi. For more options, visit https://groups.google.com/d/optout.
