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    Re: iscsi : default iscsi mode page settings.



    Julian,
    
    The FirstBurstSize is governing an iscsi parameter which is : "how much un-solicited
    data can the initiator send" ? I concur with Charles' suggestion that FirstBurstSize be
    moved to a login key.
    
    By doing this, we can improve scan times, due to the elimination of the mode
    sense/select & avoid the side effects of shared mode pages. This allows easier use of
    un-solicited data.
    
    Regards,
    Santosh
    
    Julian Satran wrote:
    
    > Separation of parameters was made on a (very good) sugestion made by Robert
    > Snively - to keep SCSI affecting values (SCSI buffer sizes etc.) in mode
    > pages and iSCSI related in key=value.
    >
    > Julo
    >
    >
    >                     "Binford,
    >                     Charles"             To:     IPS Reflector <ips@ece.cmu.edu>
    >                     <CBinford@piru       cc:
    >                     s.com>               Subject:     RE: iscsi : default iscsi mode
    >                     Sent by:              page settings.
    >                     owner-ips@ece.
    >                     cmu.edu
    >
    >
    >                     21-09-01 16:54
    >                     Please respond
    >                     to "Binford,
    >                     Charles"
    >
    >
    >
    > Santosh,  I fully agree with the intent of your comments.  One small
    > problem, however, is you argue for FirstBurstSize = 0.  Based on your other
    > comments I believe you are saying first burst should be disabled.  SPC-2
    > (and I see nothing in iSCSI to change this) defines firstBurstSize of 0 to
    > mean "no limit".  I believe that is exactly the opposite of what your are
    > arguing for.  The mode page field of firstFirstSize does not have or need
    > the concept of zero blocks allowed because the feature is is enabled /
    > disabled via other methods; process login parameters in FCP, initialR2T and
    > ImmediateData text parameters.
    >
    > So, we have the problem of how does a host that wants to use immediate or
    > unsolicited data know how much he can send.  Options I see are:
    > - define a default value for the mode page (current method in iSCSI spec).
    >   As I argued in previous posting, I believe this breaks basic mode page
    > concepts of SCSI.
    >
    > - force the host to issue a mode sense before the first command with
    > Data-Out.
    >   Not desirable, as Santosh argued in another email.
    >
    > - specify the amount of data the host send before the R2T during login as a
    > text parameter
    >   What I prefer.
    >
    > If we go with the last choice, then one has the question of what to do with
    > firstBurstSize in the mode page. Two options come to mind:
    > - reflect the login specified value in firstburstsize during mode sense.
    >   Memory says this is how it used to be?
    >
    > - do nothing with it.  Let iSCSI say that parameter in the mode page has no
    > meaning for the iSCSI protocol.  Move the "firstBurstSize" concept to the
    > iSCSI login/text parameters and let it stay there, don't try to tie it in
    > to
    > the mode pagan at all.  (my preferred choice)
    >
    > Charles Binford
    > Pirus Networks
    > 316.315.0382 x222
    >
    > -----Original Message-----
    > From: Santosh Rao [mailto:santoshr@cup.hp.com]
    > Sent: Thursday, September 20, 2001 6:44 PM
    > To: IPS Reflector
    > Subject: RE: iscsi : default iscsi mode page settings.
    >
    > All,
    >
    > I think we need to discuss the 2 issues of login key defaults & mode page
    > defaults seperately :
    >
    > 1) Defaults on login keys :
    > ===================
    > I am in favor of defining conservative defaults. Those initiators needing
    > additional features should be prepared to do the additional work of
    > negotiating those keys. It should'nt be the other way around.
    > Thus, default settings should be :
    >
    > MaxConnections = 1
    > FMarker = "no"
    > InitialR2T = "yes"
    > BidiInitialR2T = "yes"
    > ImmediateData = "no"
    > DataPDULength = 16
    > MaxOutstandingR2T = 1
    > DataPDUInOrder = "yes"
    > ErrorRecoveryLevel = 0
    > SessionType = "normal"
    >
    > I'd like to propose one more change that the LogoutLoginMinTime &
    > LogoutLoginMaxTime login keys be removed from the login keys.
    >
    > This is because these key values are only relevant for an initiator
    > re-login
    > following a target originated logout or connection drop (signalled through
    > an async message). The async message does contain these values and thus, it
    > provides no additional value to negotiate these during login.
    >
    > Also to be noted is that LogoutLoginMinTime & LogoutLoginMaxTime are most
    > likely properties of the target device (how long array "xyz" goes out to
    > lunch during certain infamous conditions) as opposed to a value that can be
    > negotiated on a per-initiator basis.
    >
    > 2) Defaults on iscsi mode pages :
    > ========================
    > Typically, no protocol defaults are specified for mode page settings.
    > Initiators should be able to function correctly without having to do either
    > mode select or mode sense. Any initiator that needs advanced settings
    > should
    > be prepared to do the extra work of issuing mode sense/select to enable
    > these features. It should NOT be the other way around. (i.e. simple
    > initiators should NOT have to first issue a mode select in order to ensure
    > proper operation of their sessions).
    >
    > If the draft does wish to profile a set of recommended defaults for the
    > iscsi, these should be conservative, where they affect the operation of
    > those initiators that do not wish to perform mode select.
    >
    > In particular, the following defaults are required, if it is decided to
    > recommend a profile of default mode page settings :
    >
    > Disconnect-Reconnect Mode Page
    > --------------------------
    >
    >    * EMDP = 0
    >
    >    * MaximumBurstSize = 512 units (as it currently defined. Targets can
    >      request less data in its R2T and send shorter data-in sequences, if
    >      mode select is not used by initiators to reduce this value.)
    >
    >    * FirstBurstSize = 0
    >
    > The FirstBurstSize ***MUST*** be set to 0 and any initiators wishing to use
    > solicited data MUST first perform mode sense/select operations to query/set
    > these values. The above default setting of 128 is  in-appropriate since :
    >
    > a) it can cause erroneous behaviour for those initiators that do not
    > perform
    > mode select to explicitly turn it off, since targets for which un-solicited
    > data is enabled but not used may reject/abort the I/O.
    >
    > b) it forces targets to ensure that 128 * 512 = 64K of un-solicited data is
    > allowed for every logged-in initiator and they have no control over turning
    > this off, since mode select is an initiator-driven operation.
    > Closing the command window causes performance drops and is not a very
    > satisfactory solution to this problem.
    >
    > Logical Unit Control Mode Page
    > ========================
    > This mode page definition can be removed from the iscsi draft since it
    > governs per-LUN state information and LUN state is the realm of the
    > SCSI ULP. In particular, it is the SCSI ULP that decides whether to
    > enable/disable CRN, since CRN is generated by the SCSI ULP.
    >
    > Thus, it is un-clear why the "Enable CRN" is negotiated at a protocol level
    > & not at a SCSI ULP mode page such as the Control Mode Page. (??).
    >
    > Could anybody comment on why CRN (a ULP feature) needs to be enabled in an
    > iscsi protocol mode page ?
    > Perhaps, for FCP it made sense to negotiate something like "Enable CRN" in
    > FCP specific mode pages, since early revisions of FCP did'nt specify the
    > CRN
    > field in FCP_CMD IU and so, the "Enable Precise Delivery" (EPDC) bit was
    > required to be queried/set using mode sense/select, prior to using CRN.
    >
    > Since iscsi supports CRN in its scsi command pdu from its initial rev, I
    > don't see why "Enable CRN" is needed to be done at the iscsi protocol
    > level.
    > (?).
    >
    > Regards,
    > Santosh
    >
    > "KRUEGER,MARJORIE (HP-Roseville,ex1)" wrote:
    >
    > > I vote for making the exchange of some text parameters MANDATORY, with no
    > > defaults.
    > >
    > > Marj
    > >
    > > > -----Original Message-----
    > > > From: Robert Snively [mailto:rsnively@Brocade.COM]
    > > > Sent: Thursday, September 20, 2001 10:48 AM
    > > > To: 'Sanjeev Bhagat (TRIPACE/Zoetermeer)'; 'Santosh Rao'; IPS
    > > > Reflector
    > > > Subject: RE: iscsi : default iscsi mode page settings.
    > > >
    > > >
    > > > It is true that default mode settings for Mode Pages
    > > > are usually arranged between buyer and vendor for
    > > > maximum convenience in the buyer's systems.  It is
    > > > generally true that any setting of a Mode Page will
    > > > allow the protocol to operate correctly, except a few,
    > > > notably the first burst size parameter if
    > > > ImmediateData is set to yes.
    > > >
    > > > On the other hand, some of the iSCSI text keyed
    > > > parameters MUST be known before the protocol will
    > > > operate correctly.  ImmediateData is certainly
    > > > one of those.  As a result, you have two choices:
    > > >
    > > >    a) Make the negotiation of all such parameters
    > > >       MANDATORY during the login and after any
    > > >       reset that may change them,  or;
    > > >
    > > >    b) Define a default state that will be guaranteed
    > > >       unless and until the parameter has been explicitly
    > > >       changed.
    > > >
    > > > Your choice.
    > > >
    > > > Bob
    > > >
    > > > > -----Original Message-----
    > > > > From: Sanjeev Bhagat (TRIPACE/Zoetermeer)
    > > > [mailto:sbhagat@tripace.com]
    > > > > Sent: Thursday, September 20, 2001 6:59 AM
    > > > > To: 'Santosh Rao'; IPS Reflector
    > > > > Subject: RE: iscsi : default iscsi mode page settings.
    > > > >
    > > > >
    > > > > Santosh,
    > > > >
    > > > > Where did you find these SCSI Mode page settings? At least I
    > > > > could not find
    > > > > it in SAM-2 document? The mode select command is available in
    > > > > SPI documents
    > > > > but they are meant for particular SCSI device and not for
    > > > > iSCSI device?
    > > > >
    > > > > Be it whatever the case I would like to ask why the default value of
    > > > > MaximumBurstSize is 512 units and why is the default value of
    > > > > FirstBurstSize
    > > > > 128 units. remember each unit is 512 bytes as defined in iSCSI 7.9x
    > > > > revisions so setting the default value of FirstBurstSize to
    > > > > 128 units means
    > > > > 65536 bytes or 64K Bytes and similarly the value of
    > > > > Maximumburstsize is 256K
    > > > > Bytes. Is it Ok to have the FirstBurstsize of 64KB??
    > > > >
    > > > > Sanjeev
    > > > >
    > > > > -----Original Message-----
    > > > > From: Santosh Rao [mailto:santoshr@cup.hp.com]
    > > > > Sent: Thursday, September 20, 2001 2:04 AM
    > > > > To: IPS Reflector
    > > > > Subject: iscsi : default iscsi mode page settings.
    > > > >
    > > > >
    > > > > All,
    > > > >
    > > > > Speaking on the subject of default settings, some questions
    > > > on recent
    > > > > changes to the iscsi mode select pages......
    > > > >
    > > > > 1) Section 3 of rev 7.94 of the iscsi draft attempts to call
    > > > > out default
    > > > > values for the iscsi  mode pages. Per my understanding, there are no
    > > > > defaults for SCSI mode pages, and all the setting are assumed to be
    > > > > disabled, unless explicitly turned on/enabled through a mode select.
    > > > >
    > > > > IOW, the keys in scsi mode pages are defined to be enabling certain
    > > > > features and the default settings are that these features are
    > > > > turned off
    > > > > unless a mode select is explicitly used to enable them.
    > > > >
    > > > > However, the iscsi mode pages seems to be using the opposite
    > > > > policy and
    > > > > is advertising default settings for mode pages, that too,
    > > > > agreesive ones
    > > > > at that! IOW, an initiator implemenation has to explicitly
    > > > > issue a mode
    > > > > select to disable/turn_off features rather than issue a
    > > > mode select to
    > > > > turn them on.
    > > > >
    > > > > Here's a few examples :
    > > > >
    > > > >    * default MaximumBurstSize : 512 units
    > > > >    * default EMDP : 1 (i.e. modify data pointers is enabled
    > > > by default
    > > > > !)
    > > > >    * default FirstBurstSize : 128 units. (i.e. initiators MUST use
    > > > > solicited
    > > > >      data, unless they explicitly turn it off using mode
    > > > > select, since,
    > > > > not
    > > > >      sending solicited data when it has been negotiated
    > > > > implies a target
    > > > > may
    > > > >      abort the I/O.
    > > > >
    > > > > I suggest that in keeping with the scsi mode pages, NO
    > > > > default settings
    > > > > be advertised for any iscsi mode
    > > > > pages. i.e. all defaults are conservative (set to 0), unless
    > > > > explicitly
    > > > > turned on thru a mode select.
    > > > >
    > > > > Comments ?
    > > > >
    > > > > Regards,
    > > > > Santosh
    > > > >
    > > > > "Mallikarjun C." wrote:
    > > > >
    > > > > > Matthew,
    > > > > >
    > > > > > I completely agree that the default should be "no"!  I
    > > > pointed this
    > > > > > out sometime ago myself.  Apart from what you point out,
    > > > the default
    > > > > > setting for "ImmediateData" seems to be at variance with the
    > > > > > conservative default for "InitialR2T" ("yes").
    > > > > >
    > > > > > Julian, could you please consider this request?
    > > > > >
    > > > > > Regards.
    > > > > > --
    > > > > > Mallikarjun
    > > > >
    > > > > > "BURBRIDGE,MATTHEW (HP-UnitedKingdom,ex2)" wrote:
    > > > > > >
    > > > > > > Julian,
    > > > > > >
    > > > > > > Appendix D24 (ImmediateData) does not describe the result of
    > > > > negotiation if
    > > > > > > the two sides differ. I presume that since the default is "yes",
    > > > > then only
    > > > > > > if both sides agree to "no" is immediate data turned
    > > > off.  Please
    > > > > can this
    > > > > > > be stated.
    > > > > > >
    > > > > > > Additionally, I feel that the default value for
    > > > > ImmediateData should
    > > > > be
    > > > > > > "no".
    > > > > > >
    > > > > > > Similarly, there is no statement on MaxOutstandingR2T.
    > > > Presumable
    > > > > the
    > > > > > > minimum is selected.
    > > > >
    > > > >
    > > >
    
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    n:Rao;Santosh 
    tel;work:408-447-3751
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    org:Hewlett Packard, Cupertino.;SISL
    adr:;;19420, Homestead Road, M\S 43LN,	;Cupertino.;CA.;95014.;USA.
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    title:Software Design Engineer
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    end:vcard
    


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