Hi Christian,
Actual test commands are below.
write: dd if=/dev/zero of=/dev/rb0 bs=4096
read: dd if=/dev/rb0 of=/dev/null bs=4096
I will check ceph readahead too.
Best regards,
On Dec 22, 2016 09:40, "Christian Balzer" <chibi@xxxxxxx> wrote:
Hello,
On Thu, 22 Dec 2016 09:12:44 +0700 Lazuardi Nasution wrote:
> Hi Christian,
>
> Thank you for your explanation. Based on your suggestion, I have put
> writeback cache-mode. But, currently the write ops is more better than read
> ops. I mean "dd if=/dev/zero of=/dev/rb0" is more better than "dd
> if=/dev/rb0 of=/dev/null". Do you know what's wrong here?
>
You may want to spend some time on figuring out what tools to use for
testing and also what your testing aims are.
As in, bandwidth or IOPS, most people tend to run into IOPS limitations
long before they run out of bandwidth.
FIO gives you a much better control over what you're testing and how.
Are the above "dd"s your actual full command lines?
So you read and wrote the entire device?
Actual results instead of "better" would be nice, too.
Either way, Ceph is known to be "slow" when doing sequential reads, google
"ceph readahead".
Also without specifying otherwise, your results are also skewed by the
pagecache and don't necessarily reflect actual Ceph performance.
Christian
> Best regards,
>
> On Dec 22, 2016 08:57, "Christian Balzer" <chibi@xxxxxxx> wrote:
>
> >
> > Hello,
> >
> > On Thu, 22 Dec 2016 01:47:36 +0700 Lazuardi Nasution wrote:
> >
> > > Hi,
> > >
> > > I'm looking for the way of setting up read only cache tier but the
> > updated
> > > objects to the backend store must be evicted from the cache (if any on
> > the
> > > cache) and it should be promoted to cache again on next miss read. This
> > > will make the cache never contain stale objects. Which cache-mode should
> > I
> > > use? Any other configuration related to this case?
> > >
> > > I have read about read-only, read-forward, read-proxy, proxy and forward
> > > cache-modes. But, I'm not so sure about the different ans which one is
> > > right for this case. I don't use write-back cache mode since writing
> > > operations has been accelerated by SSD journals.
> > >
> > >
> > If you read:
> > http://docs.ceph.com/docs/jewel/rados/operations/cache- tiering/
> >
> > you'll have seen the dire warnings about read-only mode, which can deliver
> > stale data.
> >
> > I can't think of any configuration options with read-only that wouldn't
> > (potentially) negate all performance improvements and still leave a small
> > window of staleness.
> >
> > If you have mutable data and need consistency AND want to read from the
> > cache-tier, write-back is your only valid option.
> >
> > With careful tuning you should be able to avoid having writes go to the
> > cache for objects that aren't already in it.
> >
> > Christian
> > --
> > Christian Balzer Network/Systems Engineer
> > chibi@xxxxxxx Global OnLine Japan/Rakuten Communications
> > http://www.gol.com/
> >
--
Christian Balzer Network/Systems Engineer
chibi@xxxxxxx Global OnLine Japan/Rakuten Communications
http://www.gol.com/
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