Nobody explains why, I will tell you from direct experience: the cache tier has a block size of several megabytes. So if you ask for one byte that is not in cache some megabytes are read from disk and, if cache is full, some other megabytes are written from cache to the EC pool.
Il giorno gio 28 dic 2017 alle ore 20:54 Karun Josy <karunjosy1@xxxxxxxxx> ha scritto:
Hello David,Thank you!We setup 2 pools to use EC with RBD. One ecpool and other normal replicated pool.However, would it still be advantageous to add a replicated cache tier in front of an EC one, even though it is not required anymore? I would still assume that replication would be less intensive than EC computing?Karun Josy_______________________________________________On Wed, Dec 27, 2017 at 3:42 AM, David Turner <drakonstein@xxxxxxxxx> wrote:Please use the version of the docs for your installed version of ceph. Now the Jewel in your URL and the Luminous in mine. In Luminous you no longer need a cache tier to use EC with RBDs.
http://docs.ceph.com/docs/luminous/rados/operations/cache-tiering/
On Tue, Dec 26, 2017, 4:21 PM Karun Josy <karunjosy1@xxxxxxxxx> wrote:_______________________________________________Hi,We are using Erasure coded pools in a ceph cluster for RBD images.Ceph version is 12.2.2 Luminous.----------Here it says we can use a Cache tiering infront of ec pools.To use erasure code with RBD we have a replicated pool to store metadata and ecpool as data pool .Is it possible to setup cache tiering since there is already a replicated pool that is being used ?Karun Josy
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