Le mercredi 13 mars 2013 15:44:04 UTC+1, hare a écrit : > > On 03/12/2013 11:30 PM, Mike Christie wrote: > > On 03/12/2013 08:11 AM, Guillaume wrote: > >> Hello Mike > >> > >> On 12 mar, 02:54, Mike Christie <[email protected]> wrote: > >>> On 03/09/2013 05:58 AM, Guillaume wrote: > >>> > >>>> Hello, > >>> > >>>> I have a virtual tape library and a iscsi SAN. All have multiple > >>>> ethernet interfaces, This will ressult in multiples sessions to the > >>>> targets.So I wonder if I must use dm-multipath or not ? Does the > current > >>> > >>> Does the device show up as a tape device or a block device? > >>> > >> > >> The VTL device emulates robotics, LTO cartridges and LTO5 tape drives. > >> The SAN is a block device. > > > > Are you using SCST or TGT or LIO for this? > > > >> > >>>> iscsi layer handle the multiple paths to an iqn or not ? > >>> > >>>> Another question about the output of "iscsiadm -m session" : the > lines > >>>> of output begins by @IP:3260,n where n is an integer. Is this number > a > >>>> priority level in some way, or does it only distinguish multiple > >>>> sessions to the same iqn ? > >>> > >>> It is the iSCSI target portal group number. It is assigned by the > >>> target. You can use it to group portals together. If the initiator and > >>> target supports MC/s you could then do a iSCSI level multipathing > called > >>> MC/s over portals with the same target portal group number. open-iscsi > >>> does not support MC/s > >>> > >>> > >> > >> So what I understand is that I must use md-multipath to handle the > > > > Use dm-multipath. md-multipath is older and does not have as many > features. > > > > Be _very_ cautious when using multipath on tapes. > Tapes rely on precise I/O sequencing, but multipath only guarantees > sequential I/O _submission_ at the initiator side. > If multipath decides to requeue I/O to a different path because one path > is blocked your tape is hosed. >
And how would you handle the loss of one path to the target without multipath ? At this time I have configured my system without multipath but I then access to tapes drives by only one path. If the iscsi path is lost I will have to manually switch over to use the other path. > > I'm not saying it cannot be handled, I'm just saying we haven't tested > this properly. And certainly didn't implement any precautions to avoid > this. > > But this would be best discussed on the dm-devel list. > > Cheers, > > Hannes > -- 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/open-iscsi?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
