MIR or not to MIR (TCM or "LIO") tools

[James Page]

Hi Christian

On Mon, Feb 24, 2020 at 1:51 PM Christian Ehrhardt <
christian.ehrhardt at canonical.com> wrote:

>
>
> On Tue, Feb 18, 2020 at 3:23 AM Rafael David Tinoco <
> rafaeldtinoco at ubuntu.com> wrote:
>
>> Hello all,
>>
>> I have always used TGT project, despite its bad performance, as iSCSI
>> target in Linux, offering iSCSI luns for HA clusters. It was known to me
>> that TGT was *not* the best iSCSI target supported in Linux, being LIO
>> the chosen project for that (now called TCM:
>> https://www.kernel.org/doc/Documentation/target/tcmu-design.txt).
>>
>> In a recent need, I needed SCSI 3 reservations in those SCSI volumes, to
>> test and enable fence_scsi agent, and was getting unclear errors when
>> trying to reserve the LUNs.
>>
>> The following commands - that would register a reservation key, reserve
>> a lun, release the reservation and unregister the key - don't work when
>> using TGT iSCSI luns with open-scsi and iscsid tool/service.
>>
>> $ sg_persist -r /dev/sda
>> $ sg_persist --out --register --param-sark=123abc /dev/sda
>> $ sg_persist --out --reserve --param-rk=123abc --prout-type=5 /dev/sda
>>
>> prout-type = 5 -> executes SCSI PERSISTENT RESERVE OUT (5Fh) command
>>                   with the PREEMPT AND ABORT (05h) service
>>
>>    (https://bugs.launchpad.net/ubuntu/+source/tgt/+bug/1863688)
>>
>> $ sg_persist --out --release --param-rk=123abc --prout-type=5 /dev/sda
>> $ sg_persist --out --register --param-rk=123abc /dev/sda
>>
>> With that, its impossible to fence iSCSI luns using corosync/pacemaker
>> clusters.
>>
>> TCM (or LIO) project fully supports fencing and several other iSCSI
>> features. It also supports userland backends that can extend backing
>> devices so it supports: qcow2, ceph, etc...
>>
>> Despite being HA only or not, this use case is actually being used in
>> this email to show the need to have a tool that configures kernel TCM
>> (or LIO) capability as a supported tool (at least IMO).
>>
>> I have found a recent previous MIR attempt of 1/3 of what is needed:
>>
>> https://bugs.launchpad.net/ubuntu/+source/python-rtslib-fb/+bug/1854362
>>
>> But, afaict, we would need MIRs for:
>>
>> - python3-configshell-fb
>> - python3-rtslib-fb
>> - targetcli-fb
>>
>> To have the "targetcli" tool in [main]. Upstream projects are hosted
>> together with open-iscsi repository, suggesting that they are actively
>> maintained and in good shape.
>>
>> Has this ever been discussed ? It looks to me something we could/should
>> have in 20.04. Thoughts ?
>>
>
> IIRC cinder-volume was the last bit holding back a switch.
> $ reverse-depends -r focal tgt
> Reverse-Depends
> ===============
> * cinder-volume
> * tgt-rbd [amd64 arm64 armhf ppc64el s390x]
>
> And at least cinder-volume is in main.
> So we'd have to have that changed to make the switch (as we should have
> only one supported iSCSI in main).
>
> IIRC that was also the reason we waited on last time and checking the bug
> [1] confirms similar thoughts.
> It seems you are working with jamespage already to make that switch happen.
>

I have a branch prepared for cinder to switch over the default iSCSI target
helper to LIO.


>
> Also security needs to process all the extra packages in just three days -
> unlikely right?
>
> IMHO while I agree It would be nice for 20.04 but if it is not doable in
> time due to all these constraints it is ok as well to "just" target 20.10
> with it.
> Please be on the same page with @Josh Powers <josh.powers at canonical.com> on
> this as this will be quite an intense ride to be squeezed into 20.04.
>
> P.S. FYI another reason in the past was maas but they are in a snap now
> and use their "own" tgt, so no dependency to consider anymore.
> P.P.S. have you asked (TBH I'd not know where) if some of our primary
> charms might depend on tgt?
>
> [1]:
> https://bugs.launchpad.net/ubuntu/+source/python-rtslib-fb/+bug/1854362/comments/17
>
>
> Thanks!
>>
>> Rafael
>>
>> --
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>
>
>
> --
> Christian Ehrhardt
> Staff Engineer, Ubuntu Server
> Canonical Ltd
> --
> ubuntu-server mailing list
> ubuntu-server at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/ubuntu-server
> More info: https://wiki.ubuntu.com/ServerTeam
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