On Sat, Mar 10, 2018 at 10:11 AM, shadow_lin <shadow_lin@xxxxxxx> wrote:
> Hi Jason,
>
>>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.
>
> I can get during the new active target gateway was talking to rbd the old
> active target gateway cannot write because of the RBD exclusive-lock
> But after the new target gateway done the writes,if the old target gateway
> had some blocked io during the failover,cant it then get the lock and
> overwrite the new writes?
Negative -- it's blacklisted so it cannot talk to the cluster.
> PS:
> Petasan say they can do active/active iscsi with patched suse kernel.
I'll let them comment on these corner cases.
> 2018-03-10
> ________________________________
> shadowlin
>
> ________________________________
>
> 发件人：Jason Dillaman <jdillama@xxxxxxxxxx>
> 发送时间：2018-03-10 21:40
> 主题：Re: [ceph-users] iSCSI Multipath (Load Balancing) vs RBD Exclusive Lock
> 收件人："shadow_lin"<shadow_lin@xxxxxxx>
> 抄送："Mike Christie"<mchristi@xxxxxxxxxx>,"Lazuardi
> Nasution"<mrxlazuardin@xxxxxxxxx>,"Ceph Users"<ceph-users@xxxxxxxxxxxxxx>
>
> On Sat, Mar 10, 2018 at 7:42 AM, shadow_lin <shadow_lin@xxxxxxx> 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 <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.
>>>
>>>
>>>
>>>
>>
>>
>> _______________________________________________
>> ceph-users mailing list
>> ceph-users@xxxxxxxxxxxxxx
>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>>
>
> [1] http://docs.ceph.com/docs/master/rbd/iscsi-overview/
>
> --
> Jason
--
Jason
