iSCSI:SCSI Mode Pages

Sanjeev Bhagat (TRIPACE/Zoetermeer) iscsi_t10 at sanjeevbhagat.com
Wed Sep 19 06:56:28 PDT 2001


* From the T10 Reflector (t10 at t10.org), posted by:
* "Sanjeev Bhagat \(TRIPACE/Zoetermeer\)" <iscsi_t10 at sanjeevbhagat.com>
*

 I agree with Bob.So basically you would like to say that option no. 2
referred by me was correct. The data is stored in external buffers only and
not trasnferred to the SCSI LU untill the buffer is full with ordered data.

But now my question comes whether the iSCSI target will have a common
externa buffer and it will allocate a part of  buffer for each SCSI LU
inside or is the every SCSI LU going to maintain its own buffers.

Is it also possible for 2 different SCSI LUs to negotiate EMDP bit 0 and 1

Sincerely,

Sanjeev Bhagat

Tripace Europe

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----- Original Message -----
From: "Robert Snively" <rsnively at Brocade.COM>
To: <Gerry.Houlder at seagate.com>; <t10 at t10.org>
Sent: Wednesday, September 19, 2001 2:00 AM
Subject: RE: iSCSI:SCSI Mode Pages


> * From the T10 Reflector (t10 at t10.org), posted by:
> * Robert Snively <rsnively at brocade.com>
> *
> Note that in either case questioned by Sanjeev, it is the
> TARGET,  NOT the INITIATOR, that decides in what order the
> tranfers will be performed.
>
> In the case of a READ, EMDP = 1 allows non-contiguous setting
> of the Buffer Offset parameter.
>
> In the case of a WRITE, EMDP = 1 allows non-contiguous setting
> of the R2T Buffer Offset parameter.
>
> The target will never do such things unless it has
> committed to the proper manipulation of the data by allowing
> the EMDP bit to be set to a value other than 0.
>
> Bob Snively                        e-mail:    rsnively at brocade.com
> Brocade Communications Systems     phone:  408 487 8135
> 1745 Technology Drive
> San Jose, CA 95110
>
>
>
> > -----Original Message-----
> > From: Gerry.Houlder at seagate.com [mailto:Gerry.Houlder at seagate.com]
> > Sent: Tuesday, September 18, 2001 3:25 PM
> > To: t10 at t10.org
> > Subject: Re: iSCSI:SCSI Mode Pages
> >
> >
> > * From the T10 Reflector (t10 at t10.org), posted by:
> > * Gerry.Houlder at seagate.com
> > *
> >
> > The bit is intended to allow targets to send Modify Data
> > pointer messages,
> > which is the only mechanism to allow transmitting data out of
> > order. Data
> > that is not in order is required to be preceded with this
> > message, which
> > contains an offset to the data pointer to indicate where in
> > the data stream
> > the chunk of data belongs. This feature is considered a pain
> > to implement
> > and ususally isn't supported on most devices anyway.
> >
> > If you still think you want to try this out, generally the
> > Logical Unit is
> > required to buffer the data and rearrange it as needed (it
> > may not need to
> > rearrange the data, it will probably rearrange the transfer
> > to/from media
> > activity to get it organized right).
> >
> >
> >
> >
> >
> > "Sanjeev Bhagat \(TRIPACE/Zoetermeer\)" <iscsi_t10 at sanjeevbhagat.com>
> > @t10.org on 09/18/2001 01:30:03 PM
> >
> > Sent by:  owner-t10 at t10.org
> >
> >
> > To:   "IPS Refelctor" <ips at ece.cmu.edu>, "T10 Reflector" <t10 at t10.org>
> > cc:
> >
> > Subject:  iSCSI:SCSI Mode Pages
> >
> >
> > * From the T10 Reflector (t10 at t10.org), posted by:
> > * "Sanjeev Bhagat \(TRIPACE/Zoetermeer\)"
> > <iscsi_t10 at sanjeevbhagat.com>
> > *
> > I have a query regarding section 3.1.2 EMDP mode parameter.
> > Current text
> > says
> >
> > 3.1.2 E - Enable Modify Data Pointers Bit (EMDP)
> >
> >
> > ......
> >
> > If EMDP is set to 1, Data PDU sequences may be transferred in
> > any order. If
> > EMDP is set to 0, Data PDU sequences MUST be transferred
> > using continuously
> > increasing offsets.
> >
> >
> > Does this line mean that if EMDP=1 the out of order received
> > data PDUs by
> > the iSCSI target be transferred directly to the actual SCSI
> > LU (say a HDD)
> >
> > or
> >
> > does it mean that the if EMDP=1 the out of order received data PDUs be
> > stored in some external buffer provided by SCSI LU and
> > re-assembled and
> > ordered there before transferring it into the SCSI LU.
> >
> > Regards,
> >
> > Sanjeev
> >
> >
> > *
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> >
> > *
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