2018-03-10
________________________________
shadowlin
________________________________
发件人：Jason Dillaman <jdillama@xxxxxxxxxx>
发送时间：2018-03-10 21:40
主题：Re: 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: 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: 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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[1] http://docs.ceph.com/docs/master/rbd/iscsi-overview/
--
Jason
