From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dongsheng Yang Subject: Re: bcache vs flashcache vs cache tiering Date: Thu, 16 Feb 2017 16:40:18 +0800 Message-ID: <58A56572.2020503@easystack.cn> References: <58A2C72E.6090200@easystack.cn> <18e88ebb.AEEAIAHE9hIAAAAAAAAAAEtrDcsAADNJBWwAAAAAAACRXwBYotiR@mailjet.com> <1250894564.9950.1487089524556@ox.pcextreme.nl> <58A42492.1000206@easystack.cn> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <58A42492.1000206-zgCPCz31fAiwd6j6Zg/5ug@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: ceph-users-bounces-idqoXFIVOFJgJs9I8MT0rw@public.gmane.org Sender: "ceph-users" To: nick-ksME7r3P/wO1Qrn1Bg8BZw@public.gmane.org, 'Gregory Farnum' , 'Wido den Hollander' Cc: 'Ceph Users' , ceph-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: ceph-devel.vger.kernel.org BTW, is there any body using EnhanceIO? On 02/15/2017 05:51 PM, Dongsheng Yang wrote: > thanx Nick, Gregory and Wido, > So at least, we can say the cache tiering in Jewel is stable > enough I think. > I like cache tiering more than the others, but yes, there is a problem > about cache tiering in > flushing data between different nodes, which are not a problem in > local caching solution. > > guys: > Is there any plan to enhance cache tiering to solve such problem? > Or as Nick asked, is > that cache tiering fading away? > > Yang > > On 15/02/2017, 06:42, Nick Fisk wrote: >>> -----Original Message----- >>> From: Gregory Farnum [mailto:gfarnum-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org] >>> Sent: 14 February 2017 21:05 >>> To: Wido den Hollander >>> Cc: Dongsheng Yang ; Nick Fisk >>> ; Ceph Users >>> Subject: Re: [ceph-users] bcache vs flashcache vs cache tiering >>> >>> On Tue, Feb 14, 2017 at 8:25 AM, Wido den Hollander >>> wrote: >>>>> Op 14 februari 2017 om 11:14 schreef Nick Fisk : >>>>> >>>>> >>>>>> -----Original Message----- >>>>>> From: ceph-users [mailto:ceph-users-bounces-idqoXFIVOFJgJs9I8MT0rw@public.gmane.org] On >>>>>> Behalf Of Dongsheng Yang >>>>>> Sent: 14 February 2017 09:01 >>>>>> To: Sage Weil >>>>>> Cc: ceph-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; ceph-users-idqoXFIVOFJgJs9I8MT0rw@public.gmane.org >>>>>> Subject: [ceph-users] bcache vs flashcache vs cache tiering >>>>>> >>>>>> Hi Sage and all, >>>>>> We are going to use SSDs for cache in ceph. But I am not sure >>>>>> which one is the best solution, bcache? flashcache? or cache >>>>> tier? >>>>> >>>>> I would vote for cache tier. Being able to manage it from within >>>>> Ceph, instead of having to manage X number of bcache/flashcache >>>>> instances, appeals to me more. Also last time I looked Flashcache >>>>> seems unmaintained and bcache might be going that way with talk of >>>>> this new bcachefs. Another point to consider is that Ceph has had >>>>> a lot of >>> work done on it to ensure data consistency; I don't ever want to be >>> in a >>> position where I'm trying to diagnose problems that might be being >>> caused >>> by another layer sitting in-between Ceph and the Disk. >>>>> However, I know several people on here are using bcache and >>>>> potentially getting better performance than with cache tiering, so >>> hopefully someone will give their views. >>>> I am using Bcache on various systems and it performs really well. The >>> caching layer in Ceph is slow. Promoting Objects is slow and it also >>> involves >>> additional RADOS lookups. >>> >>> Yeah. Cache tiers have gotten a lot more usable in Ceph, but the use >>> cases >>> where they're effective are still pretty limited and I think in-node >>> caching has >>> a brighter future. We just don't like to maintain the global state >>> that makes >>> separate caching locations viable and unless you're doing something >>> analogous to the supercomputing "burst buffers" (which some people >>> are!), >>> it's going to be hard to beat something that doesn't have to pay the >>> cost of >>> extra network hops/bandwidth. >>> Cache tiers are also not a feature that all the vendors support in >>> their >>> downstream products, so it will probably see less ongoing investment >>> than >>> you'd expect from such a system. >> Should that be taken as an unofficial sign that the tiering support >> is likely to fade away? >> >> I think both approaches have different strengths and probably the >> difference between a tiering system and a caching one is what causes >> some of the problems. >> >> If something like bcache is going to be the preferred approach, then >> I think more work needs to be done around certifying it for use with >> Ceph and allowing its behavior to be more controlled by Ceph as well. >> I assume there are issues around backfilling and scrubbing polluting >> the cache? Maybe you would want to be able to pass hints down from >> Ceph, which could also allow per pool cache behavior?? >> >>> -Greg >> > > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >