Hi Mike,  
So for now only suse kernel with target_rbd_core and tcmu-runner can run 
active/passive multipath safely?
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? 
What mechanism should be implement to avoid the problem with active/passive and 
active/active multipath?


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
Nasution"<mrxlazuar...@gmail.com>,"Ceph Users"<ceph-users@lists.ceph.com>

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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