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.
Best regards,
On Mar 9, 2018 12:35 AM, "Jason Dillaman" <jdillama@xxxxxxxxxx> wrote:
On Thu, Mar 8, 2018 at 11:59 AM, Lazuardi NasutionHow do you figure that's safe for preventing an overwrite with old
<mrxlazuardin@xxxxxxxxx> 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.
data in an active/active path hiccup?
> ______________________________
> Best regards,
>
> On Mar 8, 2018 11:54 PM, "Mike Christie" <mchristi@xxxxxxxxxx> 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 <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@gmail.com >,"Ceph
>> > Users"<ceph-users@xxxxxxxxxx.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.
>> >
>> >
>> >
>> >
>>
>
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--
Jason
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