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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI : Review Feedback on iSCSI Rev 06Julian, Thanks for the clarification. A few additional queries below. Regards, Santosh ----------------------------------------------------------------------------------- julian_satran@il.ibm.com wrote: > 1) Suggest re-naming the following in the interests of better > clarity : > > a) Rename the ExpDataSN in SCSI Response PDU to EndDataSN as was used in > the previous version of the draft. (indicative of being the final Data > sequence > number.) > +++ Meaning has changed - 0 means none (it was fffffff before) +++ Have the semantics of ExpDataSN in the SCSI Response PDU changed (?). From the description, it sounds like it is a count of the no of READ Data PDUs sent by the target for the command. 0 implies none were sent. (no data xfer). Hence, the name EndDataSN would be fitting since it really is the last DataSN the target used for this READ I/O. > 3) Why does the new draft limit the size of text commands and nop commands > to > 4096 bytes ? What is the rationale behind the magic number selection of > 4096 ? > > Since DataPDULength is defined in units of 512 bytes, how does iSCSI deal > with > fragmentation caused due to the usage of a DataPDULength < 4K and an > attempt to > perform a 4K text , login or nop operation ? > > I believe such scenarios were discussed in an earlier thread > titled "Fragmentation & Reassembly issues in iSCSI." > (http://ips.pdl.cs.cmu.edu/mail/msg03031.html) and the resolution was to > enforce a restriction that the size of a login, nop & text operation be > limited to DataPDULength (?). > > +++ we decided to drop negotiating trivia. A fixed maximum is more > practical > and 4096 will no create inconvenience for a long time +++ > 5) Section 2.8.3 > "The data length of a text command or response SHOULD be less than > 4096 bytes." > > suggest re-wording the above to : > "The data length of a login, nop & text command or response MUST be less > than > DataPDULength. For the leading session login, the length of the login > command > MUST be less than 512 bytes." > > The above will ensure that login, text & nop operations will not result in > fragmentation. > > +++ I have a hard time understanding the argument +++ One basic question. Does DataPDULength govern the max length of SCSI Data PDUs only or all iSCSI PDUs ? This does'nt come across clearly from the definition. If this only governs SCSI Data PDUs, then, I'd suggest the following re-wrod to make it more clear in the definition on page 129 (Appendix E) : Change : "Initiator and target negotiate the maximum data payload supported for command or data PDUs in units of 512 bytes." to : "Initiator and target negotiate the maximum data payload supported for SCSI command or data PDUs in units of 512 bytes." The above issues (3) & (5) are relevant if DataPDULength governs the length of all iSCSI PDUs. > 9) Section 2.18.1 > > "Target requests logout". > > Suggest removal of the above option. A target that needs to logout would > use > either : > "Target will drop the connection" > or > "Target will drop all connections" > > The "Target requests logout" also does not allow the target to specify > which > flavor of logout it wishes to receive. It is better to remove this option > and > use only a single scheme. > > +++ The reason for introducing it was to allow a maintenance operation > (getting out a NIC card) to start > at the target. However only the initiator knows when the connects gets > quiet. This is why will have to keep this form. The other 2 are for > emergency handling +++ Why is "target will drop connection" or "target will drop all connections" not sufficient for this purpose ? In this case, the target would send the async message, drop the connection/session and abort all outstanding I/O. The initiator on seeing the async message would clean-up all outstanding I/O on that session/connection and would attempt to re-login after LogoutLoginMinTime. begin:vcard n:Rao;Santosh tel;work:408-447-3751 x-mozilla-html:FALSE org:Hewlett Packard, Cupertino.;SISL adr:;;19420, Homestead Road, M\S 43LN, ;Cupertino.;CA.;95014.;USA. version:2.1 email;internet:santoshr@cup.hp.com title:Software Design Engineer x-mozilla-cpt:;21088 fn:Santosh Rao end:vcard
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