* Pass through device support in tgt
@ 2015-06-03 2:02 Ahmed Al-Mehdi
0 siblings, 0 replies; only message in thread
From: Ahmed Al-Mehdi @ 2015-06-03 2:02 UTC (permalink / raw)
To: stgt
Hello,
I am trying to understand the passthrough device support of tgt. For
a regular block device, to create a LU I use the following command ( I
explicitly stated the default values below):
tgtadm --mode logicalunit --op new --tid 1 --lun 1 --device-type disk
--bstype rdwr --backing-store /dev/sdb
The above command takes the block device "/dev/sdb" and exports it as
LU 1 to the initiator.
- What does it mean the tgt "creates a device of type disk" Creates
where, internal to tgt?
- What is the implication of that? Is it how the SCSI commands coming
over iSCSI is treated/handled (with respect to caching, buffering,
read ahead, etct)? Or something else?
The following example is cited in the man pages for a passthrough:
tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1
--bstype=sg --device-type=pt --backing-store=/dev/sg4
- How does the "bstype" affect the handling of the SCSI commands?
Does this affect how the IO to the actual device is done (manipulated
before sending to the actual device)?
- What does it mean for the backend storage type to be sg?
Really appreciate any help / pointers.
Regards,
Ahmed.
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