Re: iSCSI Multipath (Load Balancing) vs RBD Exclusive Lock

"shadow_lin"<shadow_lin@xxxxxxx> · Sat, 10 Mar 2018 20:42:03 +0800

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?
2018-03-10 

shadowlin

  发件人：Mike Christie <mchristi@xxxxxxxxxx>
  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_lin@xxxxxxx>,"Lazuardi 
  Nasution"<mrxlazuardin@xxxxxxxxx>,"Ceph 
  Users"<ceph-users@xxxxxxxxxxxxxx>
  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 <mchristi@xxxxxxxxxx> 
  >     *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"<mrxlazuardin@xxxxxxxxx>,"Ceph 
  >     Users"<ceph-users@xxxxxxxxxxxxxx> 
  >     *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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