Re: cache tier&Journal

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thanks Oliver, does the journal need be committed twice? One is for write IO to the cache tier? the other is for write IO destaged to SATA backend pool?

2016-04-21 19:38 GMT+08:00 Oliver Dzombic <info@xxxxxxxxxxxxxxxxx>:
Hi,

afaik cache does not have to do anything with journals.

So your OSD's need journals, and for performance, you will take SSD's.

The Cache should be something faster than your OSD's. Usually SSD or NVMe.

The Cache is an extra Space in front of your OSD's which is supposed to
speed up things because the cache operate faster than the OSD's and the
cache will flush its content to the slower OSD's.

So, the cache is independent from the OSD's. And this way, from their
journals.

And, the cache >must< be on faster drives than the OSD's, otherwise you
wont see any performance increase.

--
Mit freundlichen Gruessen / Best regards

Oliver Dzombic
IP-Interactive

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Am 21.04.2016 um 13:27 schrieb min fang:
> Hi, my ceph cluster has two pools, ssd cache tier pool and SATA backend
> pool. For this configuration, do I need use SSD as journal device? I do
> not know whether cache tier take the journal role? thanks
>
>
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> ceph-users mailing list
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