Hi Jason, I understand. Thank you for your explanation.
Best regards, On Mar 9, 2018 3:45 AM, "Jason Dillaman" <jdill...@redhat.com> wrote: > On Thu, Mar 8, 2018 at 3:41 PM, Lazuardi Nasution > <mrxlazuar...@gmail.com> wrote: > > Hi Jason, > > > > If there is the case that the gateway cannot access the Ceph, I think you > > are right. Anyway, I put iSCSI Gateway on MON node. > > It's connectivity to the specific OSD associated to the IO operation > that is the issue. If you understand the risks and are comfortable > with them, active/active is a perfectly acceptable solution. I just > wanted to ensure you understood the risk since you stated corruption > "seems impossible". > > > Best regards, > > > > > > On Mar 9, 2018 1:41 AM, "Jason Dillaman" <jdill...@redhat.com> wrote: > > > > On Thu, Mar 8, 2018 at 12:47 PM, Lazuardi Nasution > > <mrxlazuar...@gmail.com> wrote: > >> Jason, > >> > >> As long you don't activate any cache and single image for single client > >> only, it seem impossible to have old data overwrite. May be, it is > related > >> to I/O pattern too. Anyway, maybe other Ceph users have different > >> experience. It can be different result with different case. > > > > Write operation (A) is sent to gateway X who cannot access the Ceph > > cluster so the IO is queued. The initiator's multipath layer times out > > and resents write operation (A) to gateway Y, followed by write > > operation (A') to gateway Y. Shortly thereafter, gateway X is able to > > send its delayed write operation (A) to the Ceph cluster and > > overwrites write operation (A') -- thus your data went back in time. > > > >> Best regards, > >> > >> > >> On Mar 9, 2018 12:35 AM, "Jason Dillaman" <jdill...@redhat.com> wrote: > >> > >> On Thu, Mar 8, 2018 at 11:59 AM, Lazuardi Nasution > >> <mrxlazuar...@gmail.com> wrote: > >>> Hi Mike, > >>> > >>> Since I have moved from LIO to TGT, I can do full ALUA (active/active) > of > >>> multiple gateways. Of course I have to disable any write back cache at > >>> any > >>> level (RBD cache and TGT cache). It seem to be safe to disable > exclusive > >>> lock since each RBD image is accessed only by single client and as long > >>> as > >>> I > >>> know mostly ALUA use RR of I/O path. > >> > >> How do you figure that's safe for preventing an overwrite with old > >> data in an active/active path hiccup? > >> > >>> Best regards, > >>> > >>> On Mar 8, 2018 11:54 PM, "Mike Christie" <mchri...@redhat.com> wrote: > >>>> > >>>> 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. > >>>> > > >>>> > > >>>> > > >>>> > > >>>> > >>> > >>> _______________________________________________ > >>> ceph-users mailing list > >>> ceph-users@lists.ceph.com > >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > >>> > >> > >> > >> > >> -- > >> Jason > >> > >> > >> > > > > > > > > -- > > Jason > > > > > > > > -- > Jason >
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