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 _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
