Microsoft iSCSI Development
Posted May 20, 2004
Chat Date: April 29, 2004
Please note: Portions of this transcript have been edited for clarity
Introduction
Moderator: JPerry (Microsoft)
Hello, Welcome to our chat on Microsoft iSCSI Development
Moderator: JPerry (Microsoft)
I'm John Perry, Microsoft MVP Lead for DDK, and your Moderator for today.
Host: Suzanne (Microsoft)
Hi, I’m Suzanne, I’m the Program Manager for iSCSI at Microsoft
Host: alan (Microsoft)
Hi, I'm Alan and am an iSCSI developer at Microsoft.
Host: Chris (Microsoft)
Hello. This is Chris. I'm a test developer working on the iSCSI project.
Moderator: JPerry (Microsoft)
So, let's go -
Start of Chat
Host: Suzanne (Microsoft)
Q: What about boot support for the MS initiator ?
A: Microsoft supports iSCSI Boot when used with an iSCSI HBA.
Host: Suzanne (Microsoft)
iSCSI Network Boot support is something we are looking at for the future but we don't have any committment at this time.
Host: Suzanne (Microsoft)
Q: Does Microsoft plan to add iSCSI target capabilities as well?
A: No, Microsoft does not have plans to release an iSCSI target for Windows. However, there are 3rd party solutions who have iSCSI targets that run on Windows today.
Host: Suzanne (Microsoft)
Q: Has Microsoft engineering or other dept deployed iSCSI in "production"
A: Yes, Microsoft has deployed iSCSI in production in various groups inside Microsoft.
Host: alan (Microsoft)
Q: When multiple connections per session with ERL=0 are supported, will the MS iSCSI initiator tear down the session if any of the connections in a session fail
A: The current iSCSI initiator only supports ERL = 0 and a single connection per session. In a future release that supports ERL = 0 and multiple connections per session then the session will be reestablished in the case of a protocol error. In the case of a connection drop then only the connection will be reestablished.
Host: Suzanne (Microsoft)
Q: Do you plan on WHQL certification of software targets?
Host: Suzanne (Microsoft)
A: We are looking into a possible qualification program for this as a possibility
Host: Suzanne (Microsoft)
Q: When will the initiator ship with the operating system or as part of a service pack?
A: The Microsoft iSCSI Software Initiator is part of Longhorn and will most likely be part of a Windows Server 2003 refresh pack.
Host: Suzanne (Microsoft)
Q: What is the plan for Initiator on WinXP Home. In other words, what is lacking in WinXP home that prevents installing MS Inititator on it
A: We are looking into supporting XP Home in the future, it's not currently part of our test matrix.
Host: Suzanne (Microsoft)
Q: when will dynamic disks be fully supported?
A: When the new version of Microsoft Volume Management is available (Longhorn, dynamic disks will be supported with iSCSI & other services)
Host: Suzanne (Microsoft)
A: In the meantime, if you need the ability to extend disks, you can use diskpart.exe to extend basic disks.
Host: alan (Microsoft)
Q: If there are outstanding commands present on the failed connection, what do you assume about those I/Os? What does the target assume about a CmdSN gap?
A: The initiator will do a reset and then do a session recovery.
Host: Suzanne (Microsoft)
Q: Is the iSNS server provided by Microsoft considered a product?
A: Yes, it is a product.
Host: alan (Microsoft)
Q: what is your support position for ERL=2
A: We are evaluating ERL=2 for a future release
Host: Suzanne (Microsoft)
Q: Is there any material from MS for iSCSI beginners which gives an introduction to iSCSI terms (e.g. explain session, connection, iqn...)? This would be helpful for marketing.
A: There is an iSCSI Whitepaper on the iscsi website: iscsi website: https://www.microsoft.com/windowsserversystem/storage/iscsi.mspx
Host: Suzanne (Microsoft)
Q: Will there be any updates to the HCT tests in the near future? Are they still beta?
A: The iSCSI HCT kits were released in November 2003. They are shipped out of band currently but will be part of HCT 12.0 and HCT 12.1
Host: Suzanne (Microsoft)
Q: Are you planning an update release of the iSCSI DDK anytime soon? The current DDK seems to have some inconsistencies in the WMI MOFs and headers.
A: We sent out an updated version 2 weeks ago. Not sure which inconsistencies you are referring to.
Host: Suzanne (Microsoft)
Q: Is MS planning on adding a management UI to the iSNS server?
A: Yes, a management UI is included in the latest beta build of iSNS. Tentative plan for release of this version is August 2004
Host: alan (Microsoft)
Q: Is there a plan to use the iSNS server to limit the devices discovered by an initiator?
A: Yes, that is the functionality supplied by Discovery Domains which is part of the Microsoft iSNS Server. Targets can also use this to limit access to initiators as well.
Host: alan (Microsoft)
Q: Can you talk about the advantages of Multiple Connections with ERL=0, w
A: Multiple connections per session allow for failover and load balancing.
Host: Chris (Microsoft)
Q: That implies that DDs are now supported in the iSNS server?
A: Yes.
Host: Suzanne (Microsoft)
Q: What is the MS preferred method for discovering the iSNS server?
A: DHCP is the easiest method for discovering the iSNS Server
Host: alan (Microsoft)
Q: I have four sessions to same 10 lun from the backend storage. After running IO for sometime, when I try to logoff all the four sessions one at a time, we notice that we can successfully logoff the three out of four sessions, but while logging off the fourth session, from the "Disk Management" windows, I see the volume disappear and then after a few seconds they start to apprear again Is this the normal behaviour?
A: In my answer I am assuming that the forth logoff fails with the error that the device is already in use. This normal behavior. What I think is happening is that the initiator service is trying to see if all devices on the session are in use. In this case some of the devices are not in use and the service removes them before logging out the session. However another device on the session is in use and so the initiator will cause them to be reenumerated. This is likely why the disks are disappearing and reappearing in disk manager.
Host: Suzanne (Microsoft)
Q: I am curious about cluster support with iSCSI, what the plan?
A: iSCSI is supported with Windows Server 2003 Clusters. We anticipate that most deployments will use Windows Server 2003. Technically iSCSI clusters work for both Windows 2000 and Windows Server and Windows Server 2003.
Host: Suzanne (Microsoft)
Q: Does iSCSI support remote boot?
A: Yes, we support remote boot for SAN for both iSCSI and fibre channel SANs, both require the use of an HBA.
Host: alan (Microsoft)
Q: Will the RTM version of iSNS remove those event log entries which indicate invalid registration?
A: No they are useful for troubleshooting.
Host: Suzanne (Microsoft)
Q: Is there a preference (for administrative reasons) to use the iSNS server for device discovery or SendTargets? Or does it depend on the type of virtualization used?
Host: Suzanne (Microsoft)
A: iSNS is the prefered method of device discovery because it scales much better than other methods and because of the additional management capabilities that it offers.
We plan to integrate iSNS with Active Directory and Radius (IAS) in the future for even better management
Host: Suzanne (Microsoft)
Q: Do you have an idea of when iSNS will go RTM?
A: The tentative plan for release of iSNS Server is August 2004.
Host: alan (Microsoft)
Q: So what you mean is the device are being removed one at a time and then iSCSI reaches to the device which is performing the IO, and then it starts to bring back the device?
A: Yes. This is to insure that a session is not logged out while I/O is occuring on any of the devices on a target.
Host: alan (Microsoft)
Q: From my upper bus filter driver attached to the iSCSI initiator, I guess I can see the devices being removed IRP_MN_REMOVE_DEVICE for those devices and sometimes I get surprise removals too this is during the fourth log off.
A: Yes, IRP_MN_REMOVE_DEVICE are expected. I am not sure about the suprise removals as I need more information about your bus filter and what its function is.
Host: Suzanne (Microsoft)
Q: Is there a user's guide available for the iSNS server for end users? (pre-release)
A: Yes, there is a user’s guide included with the Microsoft iSCSI Software Initiator download linked from <https://www.microsoft.com/windowsserversystem/storage/iscsi.mspx> it’s installed in the docs directory
Host: Chris (Microsoft)
Q: Also I have two GB ethernet adapters on my server and establish sessions on them, is there a way to query the iSCSI and find out which connections are coming from which adapter, such as if you have multiple FC HBAs you can see which devices are coming from which HBA?
A: It depends on how you created the sessions. During login, if you explicitly specify a port number to use, then you will be able to see the source IP address using the iscsicli SessionList command.
Host: Chris (Microsoft)
A: However, if you don't specify a port number, then the source IP address will show up as 0.0.0.0.
Host: alan (Microsoft)
Q: If a connection is lost for a multiple connection session, does MS initiator make a brand new connection or attempt connection recovery?
A: Make a brand new connection
Host: alan (Microsoft)
Q: Is there a way to purge the iSNS database?
A: Yes, you do "net start msiscsi /d"
Host: alan (Microsoft)
A: Sorry, I meant "net start msisns /d"
Host: Suzanne (Microsoft)
Q: Can the MS iSCSI GUI be extended to show more details on active connections, such as which port/interface?
A: We show this info in iSCSI Property Page (Device Manager). But yes - we could look at also showing that on iSCSI Control Panel Applet. Thanks for the feedback. as well
Host: alan (Microsoft)
Q: If DHCP discovery of iSNS server is preferred, does that mean you've implemented iSNS extensions as per draft IETF spec?
A: Yes, We have implement DHCP discovery as described in the IETF draft. Currently we are using DHCP vendor specific option number 43 as IANA has not yet assigned a DHCP option for iSNS.
Host: Suzanne (Microsoft)
Q: Is there a plan to extend the MS initiator GUI to allow selection of a specific portal to use in connection establishment?
A: That's something we can look into doing. Thanks for the feedback.
Host: Suzanne (Microsoft)
Q: Since both MPIO and multiple connection per session are supported by the MS initiator, in which case should MPIO be used, and where should multiple connections be used?
A: These features are actually part of the next release of the Microsoft iSCSI software initiator, and not part of the released product.
Host: Chris (Microsoft)
Q: How in iSNS do you inform a target that it needs to re-register?
A: It is the responsibility of the target to ensure that its registration is up to date. How a target does this will depend on the level of support in the target.
Host: Chris (Microsoft)
A: A target's registration will be valid for the registration period that will be returned to the target during the initial registration. To keep the registration active, the target must send a request to the server. This request can simply be a query for its current registration. If a target implements support for ESI, it need not send a request to the server as long as it receives and responds to ESI requests. The ESI interval will be returned to the target during registration. If the target does not see an ESI request within that interval, then it should send another query request to try to maintain its current registration. If one of the query requests is returned with status code of Source Unknown, then the target should assume the registration no longer exists and should re-register.
Host: Suzanne (Microsoft)
Q: Ok, so it is a theoretical questions - MPIO vs multiple connections?
A: Microsoft MPIO solution would be the most highly available, but there are conditions where you may want to use multiple connections. You could also use a combination of both, but that can be complicated to implement and troubleshoot.
Host: alan (Microsoft)
Q: Is there any documentation on how MS initiator handles session errors, timeouts or TCP connection loss? Will the current behavior change with the new SCSI model, or new OSs?
A: In these cases the initiator will perform session recovery. What new SCSI model are you asking about ?
Host: Suzanne (Microsoft)
Q: What SDK/DDK do I need to write a Management Application to interact with the MS Inititator similar to what iscsicli.exe does?
You should use the Microsoft iSCSI DDK which is available under NDA by sending mail to iscsi@microsoft.com
Host: alan (Microsoft)
Q: Under what conditions may one prefer multiple connections over MPIO?
A: There are a number of things to consider including the target capabilities (does it support multiple session and/or multiple connections), and the initiator configuration (do you have multiple HBA or do you have only the software initiator and multiple NICs). In general if you have only the software initiator then MCS is better, if you have multiple HBA then MPIO is better.
Host: alan (Microsoft)
Q: . I shall repeat my Q - can you talk about the advantages of Multiple Connections with ERL=0, what is MS's primary motivation for this feature
A: Multiple connections per session allow for failover and load balancing.
Host: alan (Microsoft)
Q: I meant on a connection failure in a multi-connection session. I think it is useful to provide a write-up to target vendors if anything other than session reestablishment is done
A: The session will be reestablished in the case of a protocol error. In the case of a connection drop then only the connection will be reestablished. We will document this clearly.
Host: alan (Microsoft)
Q: I thought availability will be better with MPIO even with the software initiator? (assuming there are multiple NICs)?
A: Microsoft MPIO may have slightly greater overhead which could be a reason for using MCS.
Moderator: JPerry (Microsoft)
Thanks for joining us today and thanks for the questions. It's time for us to go now. Please see the chats schedule for upcoming topics.
Host: Suzanne (Microsoft)
Bye - thanks everyone for joining us today !
Host: alan (Microsoft)
Thank you for your questions !
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