On 12/03/2014 15:35, John Spray wrote: > OK, in chatting about this I've been convinced that it's legitimately > separate, because the CRUSH ruleset is mutable during the lifetime of > a pool but the EC settings are not. I suppose the way we could > explain the logical separation for users is to say that the CRUSH > ruleset is mainly about location selection, whereas the EC settings > tell you about encoding within those locations. > > Can we call this something more descriptive like "EC profile" to avoid > confusion? "properties" is very generic. That makes a lot of sense :-) I'll need to ask Sage or Sam during todays' standup to have their opinion about http://tracker.ceph.com/issues/7662#note-2 . If that approach sound sensible to them I'll provide an implementation for review in the next few days. Cheers > > Cheers, > John > > > > On Wed, Mar 12, 2014 at 1:10 PM, Loic Dachary <loic@xxxxxxxxxxx> wrote: >> On 12/03/2014 13:39, John Spray wrote: >>> I am sure all of that will work, but it doesn't explain why these >>> properties must be stored and named separately to crush rulesets. To >>> flesh this out one also needs "get" and "list" operations for the sets >>> of properties, which feels like overkill if there is an existing place >>> we could be storing these things. The reason I'm taking such an >>> interest in what may seem something minor is that once this has been >>> added, we will be stuck with it for some time once external tools >>> start depending on the interface. >>> >>> The ruleset-based approach doesn't have to be more complicated for CLI >>> users, we would essentially replace any "myproperties" above with a >>> ruleset name instead. >>> >>> osd pool create mypool <pgnum> <pgpnum> <ruleset> >>> osd set ruleset-properties <ruleset> <key>=<val> [<key>=<val>...] >>> >>> The simple default cases of "pool create mypool <pgnum> <pgpnum> >>> erasure" could be handled by making sure there exist default rulesets >>> called "erasure" and "replicated" rather than having these be magic >>> words to the commands that cause ruleset creation. Rulesets currently >>> just have numbers instead of names, but it would be simpler to add >>> names to rulesets than to introduce a whole new type of object to the >>> interface. >> Here are the default parameters >> >> OPTION(osd_pool_default_erasure_code_properties, >> OPT_STR, >> "erasure-code-plugin=jerasure " >> "erasure-code-technique=reed_sol_van " >> "erasure-code-k=4 " >> "erasure-code-m=2 " >> ) // default properties of osd pool create >> >> The k and m parameters have a clear relationship with the pool size. And they also define the minimum number of items the crush ruleset must be able to provide. The other parameters relate to the code/decode functions and are better understood in the context of the OSD than crush. This is the reason why I don't see these properties as being exclusively linked to the crush ruleset or the OSD. By introducing a new set of properties associated to the erasure code feature there is no need to chose. >> >> Does that make sense ? >>> >>> John >>> >>> On Tue, Mar 11, 2014 at 2:03 PM, Loic Dachary >>> <loic.dachary@xxxxxxxxxxxxx> wrote: >>>> On 11/03/2014 13:21, John Spray wrote: >>>>> From a high level view, what is the logical difference between the >>>>> crush ruleset and the properties object? I'm thinking about how this >>>>> is exposed to users and tools, and it seems like both would be defined >>>>> as "the settings about data placement and encoding". I certainly >>>>> understand the separation internally, I am just concerned about making >>>>> the interface we expose upwards more complicated by adding a new type >>>>> of object. >>>>> >>>>> Is there really a need for a new type of properties object, instead of >>>>> storing these properties under the existing ruleset ID? >>>> These properties are used to configure the new feature that was introduced in Firefly : erasure coded pools. From a user point of view the simplest would be to >>>> >>>> ceph osd pool create mypool erasure >>>> >>>> and rely on the fact that a default ruleset will be created using the default erasure code plugin with the default parameters. >>>> >>>> If the sysadmin wants to tweak the K+M factors (s)he could: >>>> >>>> ceph osd set properties myproperties k=10 m=4 >>>> >>>> and then >>>> >>>> ceph osd pool create mypool erasure myproperties >>>> >>>> which would implicitly ask the default erasure code plugin to create a ruleset named "mypool-ruleset" after configuring it with myproperties. >>>> >>>> If the sysadmin wants to share rulesets between pools instead of relying on their implicit creation, (s)he could >>>> >>>> ceph osd create-serasure myruleset myproperties >>>> >>>> and then ceph osd set crush_ruleset as per usual. And if (s)he really wants fine tuning, manually adding the ruleset is also possible. >>>> >>>> I feel confortable explaining this but I'm probably much too familiar with the subject to be a good judge of what makes sense to someone new or not ;-) >>>> >>>> Cheers >>>> >>>>> John >>>>> >>>>> >>>>> On Sun, Mar 9, 2014 at 12:13 PM, Loic Dachary >>>>> <loic.dachary@xxxxxxxxxxxxx> wrote: >>>>>> Hi Sage & Sam, >>>>>> >>>>>> I quickly sketched the replacement of the pg_pool_t::properties map with a OSDMap::properties list of maps at https://github.com/dachary/ceph/commit/fe3819a62eb139fc3f0fa4282b4d22aecd8cd398 and explained how I see it at http://tracker.ceph.com/issues/7662#note-2 >>>>>> >>>>>> It indeed makes things simpler, more consistent and easier to explain. I can provide an implementation this week if this seems reasonable to you. >>>>>> >>>>>> Cheers >>>>>> >>>>>> -- >>>>>> Loďc Dachary, Senior Developer >>>>>> >>>>>> -- >>>>>> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in >>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>> >>>> -- >>>> Loïc Dachary, Senior Developer >>>> >> >> >> -- >> Loïc Dachary, Artisan Logiciel Libre >> >> -- Loïc Dachary, Artisan Logiciel Libre
Attachment:
signature.asc
Description: OpenPGP digital signature
