> -----Original Message-----
> From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of
> Mike Christie
> Sent: 17 March 2015 21:27
> To: Nick Fisk; 'Jake Young'
> Cc: ceph-users@lists.ceph.com
> Subject: Re: [ceph-users] tgt and krbd
>
> On 03/15/2015 08:42 PM, Mike Christie wrote:
> > On 03/15/2015 07:54 PM, Mike Christie wrote:
> >> On 03/09/2015 11:15 AM, Nick Fisk wrote:
> >>> Hi Mike,
> >>>
> >>> I was using bs_aio with the krbd and still saw a small caching
> >>> effect. I'm not sure if it was on the ESXi or tgt/krbd page cache
> >>> side, but I was definitely seeing the IO's being coalesced into
> >>> larger ones on the krbd
> >>
> >> I am not sure what you mean here. By coalescing you mean merging
> right?
> >> That is not the same as caching. Coalescing/merging is expected for
> >> both aio and rdwr.
> >
> > For being able to see caching with aio though, I think you are right
> > and there might be a case where can use buffered writes even when
> > using O_DIRECT to the rbd device. I am not too familiar with that
> > code, so let me ping a person that works here and get back to the list.
>
> I talked to the AIO person here and confirmed that the code can drop down
> to buffered writes. However, if that happens it will then make it still
look like
> O_DIRECT by making sure writes are written back and pages are invalidated.
>
> If you want I can send you a patch to also do O_SYNC when doing AIO, so we
> can make sure flushes/barriers are also done.
>
> Send me the iometer workload when you get a chance, so I can test it out
> here.
Thanks for looking into that, I've had a bit of a busy day today, I will set
a krbt+tgt lun up tomorrow and send you the iometer stuff.
>
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