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iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

  • 1.  iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 12/27/23 10:50 AM

    Anyone tried or has experience of a scenario like the following?

    Could it work?



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    Stefano Ricca
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    #PowerVM


  • 2.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 12/28/23 08:21 PM

    Dear Stefano

    I find relevant information from this IBM URL :  iSCSI disk support for VIOS at  https://www.ibm.com/docs/en/power9?topic=overview-iscsi-disk-support-vios but it contains the following statement :

    VIOS version 3.1 enables Multipath I/O (MPIO) support for the iSCSI initiator. With MPIO support, you can configure and create multiple paths to an iSCSI disk, similar to other protocols. The client logical partition can run either an AIX® or Linux® operating system.

    If this information URL is totally accurate, then it implies that your case is NOT supported. 

    This blog post on iSCSI support for PowerVM does not mention IBM i at all either :  https://community.ibm.com/community/user/power/blogs/veena-ganti1/2020/06/23/iscsi-support-on-powervm.   



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    Chance favors only the prepared mind.
    -- Louis Pasteur
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    Satid S.
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  • 3.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 12/29/23 07:54 AM

    Thank you for your contribution. I am fully aware of the URLs you mention. Also I have submitted a SCORE, but it has been rejected. I didn't find explanation on why this is not supported. Is it a matter of performance or of missing drivers or what? This is the reason why I am asking if anyone has never had experience with this kind of scenario.



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    Stefano Ricca
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    Original Message


  • 4.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/01/24 05:06 AM

    Dear Stefano

    IBM i used to support iSCSI hosting in the distant past to be used by MS Windows Server OS (IBM i hosts its virtual disk resource to Windows server as its client). My guess that IBM i does not support your scenario may be because no one develops iSCSI client part for IBM i.   But I also have a guess that you should be able to create  vSCSI disk units over iSCSI hdisk and let IBM i client LPAR use it but this is just an uneducated guess.  If this works (with or without any usage issue), it is likely that IBM does not support it.  In my past professional experience, I knew of a few IBM i customers with adventurous spirits who implemented some functions that were not support by vendors (IBM, SAP, Mocrosoft, etc.) but they work fine.   There was a reason why there were not so many of them, though.



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    Chance favors only the prepared mind.
    -- Louis Pasteur
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    Satid S.
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    Original Message


  • 5.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/02/24 07:42 AM

    Thanks again Satid, yes, in fact, I wonder why it was supported in the past and now that technology and performance evolved it is not.



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    Stefano Ricca
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    Original Message


  • 6.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/03/24 12:01 PM

    To be clear, what Satid had described is the opposite of what you are planning on doing.  That was IBM i acting as a storage host to a Windows OS.  Most likely that was to support the embedded Intel on a Power adapter devices (I cannot remember what they were called).  Those where Intel processors on a adapter card that installed in a Power systems slot and connected to the IBM i via the Power system bus.  The idea was that you could run an Intel server with Windows or Linux  and leverage the storage from your IBM i hosting virtual disk.  

    FWIW, I never actually saw one of those used as anything but a glorified ethernet adapter.

    I feel I should also echo what others have said about the performance of the iSCSI solution you are proposing.  In the absence of a dedicated iSCSI specific adapter all of that TCP/IP overhead is going to be handled by the processor in your VIOS.  In addition, your VIOS processor will also need to handle the vSCSI processing.  That means you will not get anywhere near the 25Gb bandwidth you are expecting.  Not just a little less - a LOT less.  Closer to 1G than 25G, and that will be with very high VIOS processor utilization.

    For IBM i performance, that will be catastrophic.  IBM i needs high performance I/O to perform, and you will be giving it something that performs worse than a spinning disk.  Don't forget that you will also be choking its processor as well since you will be using it for VIOS instead.

    Do yourself a favor and get a couple of Fiber Channel cards and justify it by the savings of not having to pay for more Power processors.  



    ------------------------------
    Vincent Greene
    IT Consultant
    Technology Expert labs
    IBM
    Vincent.Greene@ibm.com


    The postings on this site are my own and don't necessarily represent IBM's positions, strategies or opinions.
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    Original Message


  • 7.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/03/24 08:52 AM
    Edited by José Pina Coelho 01/04/24 06:30 AM

    In the past, I've had problems with iSCSI (AIX initiatior to Linux target), the case was "rejected" with "AIX initiators are only supported with AIX targets". (Edit:  fixed initiator/target mixup)

    Until IBM decides to support any standards-compliant combination, you're left with SCORE-based implementations.  Talk to your service representative, he's your key to get your SCORE-request re-evaluated (or at least get a reasoned answer).

    Ignoring the "supported" angles, yes, it "should" work, and in my case it did (initially), but you don't want to be the one that proposed a solution that IBM support won't support.

    Note: I'm a firm believer in standards-based work, but we need an equal commitment from *all* our suppliers.



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    José Pina Coelho
    IT Specialist at Kyndryl
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    Original Message


  • 8.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/02/24 05:43 AM

    Hi Stefano,

    From my experience "presenting" iSCSI hdisk device from VIOS to IBMi, via vSCSI client works, but I don't recommend it for any real production workload, especially if you will be pushing high IO and expect low response time.
    I have done such a config only for PoC purposes and it works. Keep in mind that if you have any issues with that non-standard configuration for IBMi you will get very hard time getting help from IBM.

    Keep in mind that even though you have 2x 25Gb ETH connectivity, compared to let's say standard 16Gb FC HBA, you will still have better performance using FCP protocol(for IBMi). iSCSI protocol is slower than FCP since it encapsulates the SCSI commands via TCP/IP(Layer 3 network) and it will cause much higher CPU utilization on the VIOS(I assume dual VIOS config). 
    This is of course assuming that the Power server hosting IBMi is in the same DC/infra as the FS5045. If the FS5045 is in different DC then performance will be even worse, but at least you will be able to use the storage over TCP/IP.

    PS

    If you decide to give it a try, be sure to use latest VIOS4.1 that is based on AIX 7.3 and contains all the latest performance features and improvements for iSCSI.

    Regards,
    Tsvetan



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    Tsvetan Marinov
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  • 9.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/02/24 07:40 AM

    Thanks Tsvetan, your experience is very precious. The idea is to have a direct connection from 25Gb adapters in the server to the ports of the FS5045. So, no switch in the middle. Surely, I take your suggestion to use the latest version of VIOS for iSCSI improvements. Thanks a lot.



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    Stefano Ricca
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    Original Message


  • 10.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/17/24 04:48 AM

    Good information Tsvetan,

    I need to test it as well. I'm very happy about iSCSI support (I think it was part one of the latest TRs). I'm not looking for iSCSI to support heavy production workload, but it can be very attractive to send backups to public Clouds or cloning/deploying IBMi LPARs. 



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    Bartlomiej Grabowski
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    Original Message


  • 11.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 01/17/24 05:24 AM

    Hi Bart,

    This article shows the configuration steps on each VIOS, how to get the iSCSI hdisk devices configured. For good performance ideally large_send and Jumbo frames(MTU=9000) should be enabled. https://www.ibm.com/docs/en/aix/7.2?topic=considerations-iscsi-performance

    https://community.ibm.com/community/user/power/blogs/veena-ganti1/2020/06/23/iscsi-support-on-powervm

    Tsvetan



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    Tsvetan Marinov
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    Original Message


  • 12.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 07/29/26 06:04 PM

    I ran across this thread and providing a follow up - July 29, 2026:
    I checked with IBM i development and as Satid indicated, IBM i doesn't support iSCSI attached storage. This was mainly due to performance. They can be presented to VIOS and then use vscsi and hdisks to present to IBM i, but understand the limitations, mainly on performance.



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    Brian Bohner
    IBM i Global Support Center
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  • 13.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 07/29/26 06:58 PM

    Well, I have tried ISCSI with IBMi in the past, with different scenarios: Storwize V7000 Gen1, Flashsystem V5010, Linux iSCSI TGT server, and also worked with Skytap (now Kyndryl Cloud Uplift).

    All my attempts were using 1Gb ethernet with multiple connections, and besides the throughput , we observed high latency, so it is not an option, for me, for production environments.

    But...

    Skytap has been using ISCSI for years in production environments, because they have their own OpenStack framework and they can get the features they need from iSCSI-based storage devices (like IBM XIV competitors). Not sure if as of today they have moved to FCP, but they have a very tight partnership with Microsoft Azure, and ISCSI-Based cloud, so...
    What I have learned is they can provide a very improved and acceptable performance using server-side caching, but still you can notice some issues with IBM i traditional workloads, and makes sense.
    A high amount of small requests to your disk backend can kill any storage subsystem when you have high latency, and iSCSI provides more than 2ms with some load.

    If we compare actual NVMe storage, internal or external (FC), with any other technology, we are talking about a consistent 0.33 ms latency.
    In the past, with mechanical hard drives (15K RPM) and good RAID adapters (1GB cache or even more), we were able to get 1ms ~ 2ms response times (always with the right sizing).
    With XIV (sorry, I never liked IBM XIV systems) from latest generations, using internal infiniband and FC to your IBM Power box, you could get worst response times than using a FlashSystem 5100 with IBM I, because of latency. I have seen 4ms to 8ms with XIV...

    My recommendations:

    • If you want to build an openstack thing, like Skytap/Kyndryl, and have enough resources, you can go on, but you won't have IBM official support.
    • If you need small development/test environments, this could be an option
    • If you need for production environments, please, don't forget the lack of IBM support.
    • If you have high I/O workloads, specially with RPG or Cobol code, try a different thing.
    • SQL workloads can get a decent response time, but you need enough resources in your VIOS.
    • If you can afford it, use a switch, to have paths from both controllers on each VIOS.

    Good luck, and please, let Us know to learn about your case!



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    Diego E. KESSELMAN
    IBM Champion
    ESSELWARE Soluciones
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    Original Message


  • 14.  RE: iSCSI disk inside VIOS assigned to IBM i client LPAR using vscsi

    Posted 08/10/26 01:41 AM

    Hi ,

    iSCSI-backed vSCSI disk to an IBM i client LPAR is not a supported configuration, even though the underlying mechanism (VIOS iSCSI initiator → hdisk → vSCSI to a client) works fine for AIX and Linux clients. IBM i's storage stack has stricter validation requirements (520-byte sector handling, specific hdisk type recognition, etc.) and iSCSI hasn't been certified against it.

    Practical implication for your diagram: if you need external SAN-attached storage virtualized to an IBM i client LPAR through VIOS via vSCSI, the supported path is Fibre Channel-attached LUNs (or NPIV), not iSCSI. If FC isn't an option and you're set on the FS5045, you'd want to confirm whether it supports FC target ports so you can swap the iSCSI leg in your diagram for FC, keeping the same VIOS → hdisk → vSCSI → IBM i client structure.

    Worth checking IBM's current SSIC and support docs directly, since these positions do occasionally get revisited - but as of that thread and the current VIOS iSCSI documentation, this isn't a supported setup for IBM i.

    Thank you 



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    Anas AlSaleh
    IBM Power Systems Software Specialist
    Saudi Business Machines ( SBM )
    Riyadh
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