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?
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/
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