Perfect ! After this reply, I had to dig deeper and now it makes sense....thanks a lot The Lee-Man for explaining it so effectively...
On Saturday, November 9, 2019 at 7:52:52 PM UTC+1, The Lee-Man wrote: > > On Friday, November 8, 2019 at 10:40:08 AM UTC-8, Bobby wrote: >> >> >> Hi Ulrich, >> >> Thanks for the hint. Can you please help me regarding following two >> questions. >> >> - Linux block layer perform IO scheduling IO submissions to storage >> device driver. If there is a physical device, the block layer interacts >> with it through SCSI mid layer and SCSI low level drivers. So, how >> *actually* a software initiator (*Open-iSCSI*) interacts with "*block >> layer*"? >> >> - What confuses me, where does the "*disk driver*" comes into play? >> >> Thanks :-) >> >> > In an iSCSI connection (session), there is the initiator and the target. I > assume you are talking about the initiator. > > On the initiator, the "magic" is done by the kernel, in particular the > iSCSI initiator code in the kernel, specifically by the > scsi_transport_iscsi.c in drivers/scsi. When an iSCSI connection is made, > the code creates a new "host" object, and then tests the device at the > other end of the connection. If it's a disc drive, then an instance of sd > is created (the disc driver). If the device is tape, a tape driver is > instantiated (st). Unrecognized devices still get a generic SCSI device > node, I believe. > > So, in this way, iSCSI is acting like an adapter driver, which plugs into > the SCSI mid-layer. > > You can run "sudo journalctl -xe --follow" in one window, then log into an > existing target in another (I used "sudo iscsiadm -m node -l"), and you > should see this kind of output from journalctl: > > ... > > > >> Nov 09 10:46:59 linux-dell kernel: iscsi: registered transport (tcp) >> Nov 09 10:46:59 linux-dell kernel: scsi host3: iSCSI Initiator over TCP/IP >> Nov 09 10:46:59 linux-dell iscsid[13175]: iscsid: Connection1:0 to >> [target: iqn.2003-01.org.linux-iscsi.linux-dell.x8664:sn.2a6e21b1b53c, >> portal: 192.168.20.3,3260] through [iface: default] is operational now >> Nov 09 10:46:59 linux-dell kernel: scsi 3:0:0:0: Direct-Access >> LIO-ORG test-disc 4.0 PQ: 0 ANSI: 5 >> Nov 09 10:46:59 linux-dell kernel: scsi 3:0:0:0: alua: supports implicit >> and explicit TPGS >> Nov 09 10:46:59 linux-dell kernel: scsi 3:0:0:0: alua: device >> naa.6001405de01c6e7933b414e901e22b0f port group 0 rel port 1 >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: Attached scsi generic sg1 >> type 0 >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] 2097152 512-byte >> logical blocks: (1.07 GB/1.00 GiB) >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Write Protect is off >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Mode Sense: 43 00 10 >> 08 >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Write cache: >> enabled, read cache: enabled, supports DPO and FUA >> Nov 09 10:46:59 linux-dell kernel: >> iSCSI/iqn.1996-04.de.suse:01:54cab487975b: Unsupported SCSI Opcode 0xa3, >> sending CHECK_CONDITION. >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Optimal transfer >> size 8388608 bytes >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Attached SCSI disk >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: alua: transition timeout >> set to 60 seconds >> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: alua: port group 00 state >> A non-preferred supports TOlUSNA >> > ... > > -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/open-iscsi/bae3a7e2-306b-4959-9f8a-62bb6ae6fb00%40googlegroups.com.
