On Sat, Mar 10, 2018 at 7:42 AM, shadow_lin <shadow_...@163.com> wrote:
> Hi Mike,
> So for now only suse kernel with target_rbd_core and tcmu-runner can run
> active/passive multipath safely?

Negative, the LIO / tcmu-runner implementation documented here [1] is
safe for active/passive.

> I am a newbie to iscsi. I think the stuck io get excuted cause overwrite
> problem can happen with both active/active and active/passive.
> What makes the active/passive safer than active/active?

As discussed in this thread, for active/passive, upon initiator
failover, we used the RBD exclusive-lock feature to blacklist the old
"active" iSCSI target gateway so that it cannot talk w/ the Ceph
cluster before new writes are accepted on the new target gateway.

> What mechanism should be implement to avoid the problem with active/passive
> and active/active multipath?

Active/passive it solved as discussed above. For active/active, we
don't have a solution that is known safe under all failure conditions.
If LIO supported MCS (multiple connections per session) instead of
just MPIO (multipath IO), the initiator would provide enough context
to the target to detect IOs from a failover situation.

> 2018-03-10
> ________________________________
> shadowlin
>
> ________________________________
>
> 发件人:Mike Christie <mchri...@redhat.com>
> 发送时间:2018-03-09 00:54
> 主题:Re: [ceph-users] iSCSI Multipath (Load Balancing) vs RBD Exclusive Lock
> 收件人:"shadow_lin"<shadow_...@163.com>,"Lazuardi
> Nasution"<mrxlazuar...@gmail.com>,"Ceph Users"<ceph-users@lists.ceph.com>
> 抄送:
>
> On 03/07/2018 09:24 AM, shadow_lin wrote:
>> Hi Christie,
>> Is it safe to use active/passive multipath with krbd with exclusive lock
>> for lio/tgt/scst/tcmu?
>
> No. We tried to use lio and krbd initially, but there is a issue where
> IO might get stuck in the target/block layer and get executed after new
> IO. So for lio, tgt and tcmu it is not safe as is right now. We could
> add some code tcmu's file_example handler which can be used with krbd so
> it works like the rbd one.
>
> I do know enough about SCST right now.
>
>
>> Is it safe to use active/active multipath If use suse kernel with
>> target_core_rbd?
>> Thanks.
>>
>> 2018-03-07
>> ------------------------------------------------------------------------
>> shadowlin
>>
>> ------------------------------------------------------------------------
>>
>>     *发件人:*Mike Christie <mchri...@redhat.com>
>>     *发送时间:*2018-03-07 03:51
>>     *主题:*Re: [ceph-users] iSCSI Multipath (Load Balancing) vs RBD
>>     Exclusive Lock
>>     *收件人:*"Lazuardi Nasution"<mrxlazuar...@gmail.com>,"Ceph
>>     Users"<ceph-users@lists.ceph.com>
>>     *抄送:*
>>
>>     On 03/06/2018 01:17 PM, Lazuardi Nasution wrote:
>>     > Hi,
>>     >
>>     > I want to do load balanced multipathing (multiple iSCSI
>> gateway/exporter
>>     > nodes) of iSCSI backed with RBD images. Should I disable exclusive
>> lock
>>     > feature? What if I don't disable that feature? I'm using TGT (manual
>>     > way) since I get so many CPU stuck error messages when I was using
>> LIO.
>>     >
>>
>>     You are using LIO/TGT with krbd right?
>>
>>     You cannot or shouldn't do active/active multipathing. If you have the
>>     lock enabled then it bounces between paths for each IO and will be
>> slow.
>>     If you do not have it enabled then you can end up with stale IO
>>     overwriting current data.
>>
>>
>>
>>
>
>
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> ceph-users@lists.ceph.com
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>

[1] http://docs.ceph.com/docs/master/rbd/iscsi-overview/

-- 
Jason
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