Re: Re: crush devices class types

[Sage Weil <sage@newdream.net>]

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On Wed, 28 Jun 2017, clive.xc@gmail.com wrote:
> Hi Sage,
> I am trying ceph 12.2.0, and got one problem:
> 
> my bucket can be created succesfully,
> 
> [root@node1 ~]# ceph osd tree
> ID WEIGHT  TYPE NAME          UP/DOWN REWEIGHT PRIMARY-AFFINITY
> -6 0.01939 root default~ssd                                    
> -5 0.01939     host node1~ssd                                  
>  0 0.01939         osd.0           up  1.00000          1.00000
> -4 0.01939 root default~hdd                                    
> -3 0.01939     host node1~hdd                                  
>  1 0.01939         osd.1           up  1.00000          1.00000
> -1 0.03879 root default                                        
> -2 0.03879     host node1                                      
>  0 0.01939         osd.0           up  1.00000          1.00000
>  1 0.01939         osd.1           up  1.00000          1.00000
> 
> but crush rule cannot be created:
> 
> [root@node1 ~]# ceph osd crush rule create-simple hdd default~hdd host
> Invalid command:  invalid chars ~ in default~hdd
> osd crush rule create-simple <name> <root> <type> {firstn|indep} :  create
?? ?crush rule <name> to start from <root>, replicate across buckets of type <t
> ype>, using a choose mode of <firstn|indep> (default firstn; indep best for
>  erasure pools)
> Error EINVAL: invalid command

Eep.. this is an oversight.  We need to fix the create rule command to 
allow rules specifying a device class.  I'll make sure this is in the next 
RC.

Until then, you can extract the crush map and create the rule manually.  
The updated syntax adds 'class <foo>' to the end of the 'take' step.  
e.g.,

rule replicated_ssd_rule {
        ruleset 1
        type replicated
        min_size 1
        max_size 10
        step take default class ssd
        step chooseleaf firstn 0 type host
        step emit
}

sage




 > 
> ____________________________________________________________________________
> clive.xc@gmail.com
>        
> From: Sage Weil
> Date: 2017-03-09 01:00
> To: Dan van der Ster
> CC: Loic Dachary; John Spray; Ceph Development
> Subject: Re: crush devices class types
> On Wed, 8 Mar 2017, Dan van der Ster wrote:
> > On Wed, Mar 8, 2017 at 3:39 PM, Sage Weil <sage@newdream.net> wrote:
> > > On Wed, 8 Mar 2017, Dan van der Ster wrote:
> > >> Hi Loic,
> > >>
> > >> Did you already have a plan for how an operator would declare the
> > >> device class of each OSD?
> > >> Would this be a new --device-class option to ceph-disk prepare,
> which
> > >> would perhaps create a device-class file in the root of the OSD's
> xfs
> > >> dir?
> > >> Then osd crush create-or-move in ceph-osd-prestart.sh would be a
> > >> combination of ceph.conf's "crush location" and this per-OSD
> file.
> > >
> > > Hmm we haven't talked about this part yet.  I see a few options...
> > >
> > > 1) explicit ceph-disk argument, recorded as a file in osd_data
> > >
> > > 2) osd can autodetect this based on the 'rotational' flag in
> sysfs.  The
> > > trick here, I think, is to come up with suitable defaults.  We
> might have
> > > NVMe, SATA/SAS SSDs, HDD, or a combination (with journal and data
> (and
> > > db) spread across multiple types).   Perhaps those could break
> down into
> > > classes like
> > >
> > >         hdd
> > >         ssd
> > >         nvme
> > >         hdd+ssd-journal
> > >         hdd+nvme-jouranl
> > >         hdd+ssd-db+nvme-jouranl
> > >
> > > which is probably sufficient for most users.  And if the admin
> likes they
> > > can override.
> > >
> > > - Then the osd adjusts device-class on startup, just like it does
> with the
> > > crush map position.  (Note that this will have no real effect
> until the
> > > CRUSH rule(s) are changed to use device class.)
> > >
> > > - We'll need an 'osd crush set-device-class <osd.NNN> <class>'
> command.
> > > The only danger I see here is that if you set it to something
> other than
> > > what the OSD autodetects above, it'll get clobbered on the next
> OSD
> > > restart.  Maybe the autodetection *only* sets the device class if
> it isn't
> > > already set?
> >
> > This is the same issue we have with crush locations, hence the osd
> > crush update on start option, right?
> >
> > >
> > > - We need to adjust the crush rule commands to allow a device
> class.
> > > Currently we have
> > >
> > > osd crush rule create-erasure <name>     create crush rule <name>
> for erasure
> > >  {<profile>}                              coded pool created with
> <profile> (
> > >                                           default default)
> > > osd crush rule create-simple <name>      create crush rule <name>
> to start from
> > >  <root> <type> {firstn|indep}             <root>, replicate across
> buckets of
> > >                                           type <type>, using a
> choose mode of
> > >                                           <firstn|indep> (default
> firstn; indep
> > >                                           best for erasure pools)
> > >
> > > ...so we could add another optional arg at the end for the device
> class.
> > >
> >
> > How far along in the implementation are you? Still time for
> discussing
> > the basic idea?
> >
> > I wonder if you all had thought about using device classes like we
> use
> > buckets (i.e. to choose across device types)? Suppose I have two
> > brands of ssds: I want to define two classes ssd-a and ssd-b. And I
> > want to replicate across these classes (and across, say, hosts as
> > well). I think I'd need a choose step to choose 2 from classtype ssd
> > (out of ssd-a, ssd-b, etc...), and then chooseleaf across hosts.
> > IOW, device classes could be an orthogonal, but similarly flexible,
> > structure to crush buckets: device classes would have a hierarchy.
> >
> > So we could still have:
> >
> > device 0 osd.0 class ssd-a
> > device 1 osd.1 class ssd-b
> > device 2 osd.2 class hdd-c
> > device 3 osd.3 class hdd-d
> >
> > but then we define the class-types and their hierarchy like we
> already
> > do for osds. Shown in a "class tree" we could have, for example:
> >
> > TYPE               NAME
> > root                  default
> >     classtype    hdd
> >         class        hdd-c
> >         class        hdd-d
> >     classtype    ssd
> >         class        ssd-a
> >         class        ssd-b
> >
> > Sorry to bring this up late in the thread.
>  
> John mentioned something similar in a related thread several weeks
> back. 
> This would be a pretty cool capability.  It's quite a bit harder to
> realize, though.
>  
> First, you need to ensure that you have a broad enough mix to device
> classes to make this an enforceable constraint.  Like if you're doing
> 3x
> replication, that means at least 3 brands/models of SSDs.  And, like
> the
> normal hierarchy, you need to ensure that there are sufficient numbers
> of
> each to actually place the data in a way that satisfies the
> constraint.
>  
> Mainly, though, it requires a big change to the crush mapping
> algorithm
> itself.  (A nice property of the current device classes is that crush
> on
> theclient doesn't need to change--this will work fine with any legacy
> client.)  Here, though, we'd need to do the crush rules in 2
> dimentions.  Something like first choosing the device types for the
> replicas, and then using a separate tree for each device, while also
> recognizing the equivalence of other nodes in the hiearachy (racks,
> hosts,
> etc.) to enforce the usual placement constraints.
>  
> Anyway, it would be much more involved.  I think the main thing to do
> now
> is try to ensure we don't make our lives harder later if we go down
> that
> path.  My guess is we'd want to adopt some naming mechanism for
> classes
> that is friendly to class hierarchy like you have above (e.g. hdd/a,
> hdd/b), but otherwise the "each device has a class" property we're
> adding
> now wouldn't really change.  The new bit would be how the rule is
> defined,
> but since larger changes would be needed there I don't think the small
> tweak we've just made would be an issue...?
>  
> BTW, the initial CRUSH device class support just merged.  Next up are
> the
> various mon commands and osd hooks to make it easy to use...
>  
> sage
>  
>  
>  
> >
> > Cheers, Dan
> >
> >
> > > sage
> > >
> > >
> > >
> > >
> > >
> > >>
> > >> Cheers, Dan
> > >>
> > >>
> > >>
> > >> On Wed, Feb 15, 2017 at 1:14 PM, Loic Dachary <loic@dachary.org>
> wrote:
> > >> > Hi John,
> > >> >
> > >> > Thanks for the discussion :-) I'll start implementing the
> proposal as described originally.
> > >> >
> > >> > Cheers
> > >> >
> > >> > On 02/15/2017 12:57 PM, John Spray wrote:
> > >> >> On Fri, Feb 3, 2017 at 1:21 PM, Loic Dachary
> <loic@dachary.org> wrote:
> > >> >>>
> > >> >>>
> > >> >>> On 02/03/2017 01:46 PM, John Spray wrote:
> > >> >>>> On Fri, Feb 3, 2017 at 12:22 PM, Loic Dachary
> <loic@dachary.org> wrote:
> > >> >>>>> Hi,
> > >> >>>>>
> > >> >>>>> Reading Wido & John comments I thought of something, not
> sure if that's a good idea or not. Here it is anyway ;-)
> > >> >>>>>
> > >> >>>>> The device class problem we're trying to solve is one
> instance of a more general need to produce crush tables that implement
> a given use case. The SSD / HDD use case is so frequent that it would
> make sense to modify the crush format for this. But maybe we could
> instead implement that to be a crush table generator.
> > >> >>>>>
> > >> >>>>> Let say you want help to create the hierarchies to
> implement the ssd/hdd separation, you write your crushmap using the
> proposed syntax. But instead of feeding it directly to crushtool -c,
> you would do something like:
> > >> >>>>>
> > >> >>>>>    crushtool --plugin 'device-class' --transform <
> mycrushmap.txt | crushtool -c - -o mycrushmap
> > >> >>>>>
> > >> >>>>> The 'device-class' transformation documents the naming
> conventions so the user knows root will generate root_ssd and
> root_hdd. And the users can also check by themselves the generated
> crushmap.
> > >> >>>>>
> > >> >>>>> Cons:
> > >> >>>>>
> > >> >>>>> * the users need to be aware of the transformation step and
> be able to read and understand the generated result.
> > >> >>>>> * it could look like it's not part of the standard way of
> doing things, that it's a hack.
> > >> >>>>>
> > >> >>>>> Pros:
> > >> >>>>>
> > >> >>>>> * it can inspire people to implement other crushmap
> transformation / generators (an alternative, simpler, syntax comes to
> mind ;-)
> > >> >>>>> * it can be implemented using python to lower the barrier
> of entry
> > >> >>>>>
> > >> >>>>> I don't think it makes the implementation of the current
> proposal any simpler or more complex. Worst case scenario nobody write
> any plugin but that does not make this one plugin less useful.
> > >> >>>>
> > >> >>>> I think this is basically the alternative approach that Sam
> was
> > >> >>>> suggesting during CDM: the idea of layering a new (perhaps
> very
> > >> >>>> similar) syntax on top of the existing one, instead of
> extending the
> > >> >>>> existing one directly.
> > >> >>>
> > >> >>> Ha nice, not such a stupid idea then :-) I'll try to defend
> it a little more below then. Please bear in mind that I'm not sure
> this is the way to go even though I'm writing as if I am.
> > >> >>>
> > >> >>>> The main argument against doing that was the complexity, not
> just of
> > >> >>>> implementation but for users, who would now potentially have
> two
> > >> >>>> separate sets of commands, one operating on the "high level"
> map
> > >> >>>> (which would have a "myhost" object in it), and one
> operating on the
> > >> >>>> native crush map (which would only have myhost~ssd,
> myhost~hdd
> > >> >>>> entries, and would have no concept that a thing called
> myhost
> > >> >>>> existed).
> > >> >>>
> > >> >>> As a user I'm not sure what is more complicated / confusing.
> If I'm an experienced Ceph user I'll think of this new syntax as a
> generator because I already know how crush works. I'll welcome the
> help and be relieved that I don't have to manually do that anymore.
> But having that as a native syntax may be a little unconfortable for
> me because I will want to verify the new syntax matches what I expect,
> which comes naturally if the transformation step is separate. I may
> even tweak it a little with an intermediate script to match one thing
> or two. If I'm a new Ceph user this is one more concept I need to
> learn: the device class. And to understand what it means, the
> documentation will have to explain that it creates an independant
> crush hierarchy for each device class, with weights that only take
> into account the devices of that given class. I will not be exonerated
> from understanding the transformation step and the syntactic sugar may
> even make that more complicated to ge
> t.
> > >> >>>
> > >> >>> If I understand correctly, the three would co-exist: host,
> host~ssd, host~hdd so that you can write a rule that takes from all
> devices.
> > >> >>
> > >> >> (Sorry this response is so late)
> > >> >>
> > >> >> I think the extra work is not so much in the formats, as it is
> > >> >> exposing that syntax via all the commands that we have, and/or
> new
> > >> >> commands.  We would either need two lots of commands, or we
> would need
> > >> >> to pick one layer (the 'generator' or the native one) for the
> > >> >> commands, and treat the other layer as a hidden thing.
> > >> >>
> > >> >> It's also not just the extra work of implementing the
> commands/syntax,
> > >> >> it's the extra complexity that ends up being exposed to users.
> > >> >>
> > >> >>>
> > >> >>>> As for implemetning other generators, the trouble with that
> is that
> > >> >>>> the resulting conventions would be unknown to other tools,
> and to any
> > >> >>>> commands built in to Ceph.
> > >> >>>
> > >> >>> Yes. But do we really want to insert the concept of "device
> class" in Ceph ? There are recurring complaints about manually
> creating the crushmap required to separate ssd from hdd. But is it
> inconvenient in any way that Ceph is otherwise unaware of this
> distinction ?
> > >> >>
> > >> >> Currently, if someone has done the manual stuff to set up
> SSD/HDD
> > >> >> crush trees, any external tool has no way of knowing that two
> hosts
> > >> >> (one ssd, one hdd) are actually the same host.  That's the key
> thing
> > >> >> here for me -- the time saving during setup is a nice side
> effect, but
> > >> >> the primary value of having a Ceph-defined way to do this is
> that
> > >> >> every tool building on Ceph can rely on it.
> > >> >>
> > >> >>
> > >> >>
> > >> >>>> We *really* need a variant of "set noout"
> > >> >>>> that operates on a crush subtree (typically a host), as it's
> the sane
> > >> >>>> way to get people to temporarily mark some OSDs while they
> > >> >>>> reboot/upgrade a host, but to implement that command we have
> to have
> > >> >>>> an unambiguous way of identifying which buckets in the crush
> map
> > >> >>>> belong to a host.  Whatever the convention is (myhost~ssd,
> myhost_ssd,
> > >> >>>> whatever), it needs to be defined and built into Ceph in
> order to be
> > >> >>>> interoperable.
> > >> >>>
> > >> >>> That goes back (above) to my understanding of Sage proposal
> (which I may have wrong ?) in which the host bucket still exists and
> still contains all devices regardless of their class.
> > >> >>
> > >> >> In Sage's proposal as I understand it, there's an underlying
> native
> > >> >> crush map that uses today's format (i.e. clients need no
> upgrade),
> > >> >> which is generated in response to either commands that edit
> the map,
> > >> >> or the user inputting a modified map in the text format.  That
> > >> >> conversion would follow pretty simple rules (assuming a host
> 'myhost'
> > >> >> with ssd and hdd devices):
> > >> >>  * On the way in, bucket 'myhost' generates 'myhost~ssd',
> 'myhost~hdd' buckets
> > >> >>  * On the way out, buckets 'myhost~ssd', 'myhost~hdd' get
> merged into 'myhost'
> > >> >>  * When running a CLI command, something targeting 'myhost'
> will
> > >> >> target both 'myhost~hdd' and 'myhost~ssd'
> > >> >>
> > >> >> It's that last part that probably isn't captured properly by
> something
> > >> >> external that does a syntax conversion during import/export.
> > >> >>
> > >> >> John
> > >> >>
> > >> >>> Cheers
> > >> >>>
> > >> >>>>
> > >> >>>> John
> > >> >>>>
> > >> >>>>
> > >> >>>>
> > >> >>>>> Cheers
> > >> >>>>>
> > >> >>>>> On 02/02/2017 09:57 PM, Sage Weil wrote:
> > >> >>>>>> Hi everyone,
> > >> >>>>>>
> > >> >>>>>> I made more updates to http://pad.ceph.com/p/crush-types
> after the CDM
> > >> >>>>>> discussion yesterday:
> > >> >>>>>>
> > >> >>>>>> - consolidated notes into a single proposal
> > >> >>>>>> - use otherwise illegal character (e.g., ~) as separater
> for generated
> > >> >>>>>> buckets.  This avoids ambiguity with user-defined buckets.
> > >> >>>>>> - class-id $class $id properties for each bucket.  This
> allows us to
> > >> >>>>>> preserve the derivative bucket ids across a
> decompile->compile cycle so
> > >> >>>>>> that data does not move (the bucket id is one of many
> inputs into crush's
> > >> >>>>>> hash during placement).
> > >> >>>>>> - simpler rule syntax:
> > >> >>>>>>
> > >> >>>>>>     rule ssd {
> > >> >>>>>>             ruleset 1
> > >> >>>>>>             step take default class ssd
> > >> >>>>>>             step chooseleaf firstn 0 type host
> > >> >>>>>>             step emit
> > >> >>>>>>     }
> > >> >>>>>>
> > >> >>>>>> My rationale here is that we don't want to make this a
> separate 'step'
> > >> >>>>>> call since steps map to underlying crush rule step ops,
> and this is a
> > >> >>>>>> directive only to the compiler.  Making it an optional
> step argument seems
> > >> >>>>>> like the cleanest way to do that.
> > >> >>>>>>
> > >> >>>>>> Any other comments before we kick this off?
> > >> >>>>>>
> > >> >>>>>> Thanks!
> > >> >>>>>> sage
> > >> >>>>>>
> > >> >>>>>>
> > >> >>>>>> On Mon, 23 Jan 2017, Loic Dachary wrote:
> > >> >>>>>>
> > >> >>>>>>> Hi Wido,
> > >> >>>>>>>
> > >> >>>>>>> Updated http://pad.ceph.com/p/crush-types with your
> proposal for the rule syntax
> > >> >>>>>>>
> > >> >>>>>>> Cheers
> > >> >>>>>>>
> > >> >>>>>>> On 01/23/2017 03:29 PM, Sage Weil wrote:
> > >> >>>>>>>> On Mon, 23 Jan 2017, Wido den Hollander wrote:
> > >> >>>>>>>>>> Op 22 januari 2017 om 17:44 schreef Loic Dachary
> <loic@dachary.org>:
> > >> >>>>>>>>>>
> > >> >>>>>>>>>>
> > >> >>>>>>>>>> Hi Sage,
> > >> >>>>>>>>>>
> > >> >>>>>>>>>> You proposed an improvement to the crush map to
> address different device types (SSD, HDD, etc.)[1]. When learning how
> to create a crush map, I was indeed confused by the tricks required to
> create SSD only pools. After years of practice it feels more natural
> :-)
> > >> >>>>>>>>>>
> > >> >>>>>>>>>> The source of my confusion was mostly because I had to
> use a hierarchical description to describe something that is not
> organized hierarchically. "The rack contains hosts that contain
> devices" is intuitive. "The rack contains hosts that contain ssd that
> contain devices" is counter intuitive. Changing:
> > >> >>>>>>>>>>
> > >> >>>>>>>>>>     # devices
> > >> >>>>>>>>>>     device 0 osd.0
> > >> >>>>>>>>>>     device 1 osd.1
> > >> >>>>>>>>>>     device 2 osd.2
> > >> >>>>>>>>>>     device 3 osd.3
> > >> >>>>>>>>>>
> > >> >>>>>>>>>> into:
> > >> >>>>>>>>>>
> > >> >>>>>>>>>>     # devices
> > >> >>>>>>>>>>     device 0 osd.0 ssd
> > >> >>>>>>>>>>     device 1 osd.1 ssd
> > >> >>>>>>>>>>     device 2 osd.2 hdd
> > >> >>>>>>>>>>     device 3 osd.3 hdd
> > >> >>>>>>>>>>
> > >> >>>>>>>>>> where ssd/hdd is the device class would be much
> better. However, using the device class like so:
> > >> >>>>>>>>>>
> > >> >>>>>>>>>>     rule ssd {
> > >> >>>>>>>>>>             ruleset 1
> > >> >>>>>>>>>>             type replicated
> > >> >>>>>>>>>>             min_size 1
> > >> >>>>>>>>>>             max_size 10
> > >> >>>>>>>>>>             step take default:ssd
> > >> >>>>>>>>>>             step chooseleaf firstn 0 type host
> > >> >>>>>>>>>>             step emit
> > >> >>>>>>>>>>     }
> > >> >>>>>>>>>>
> > >> >>>>>>>>>> looks arcane. Since the goal is to simplify the
> description for the first time user, maybe we could have something
> like:
> > >> >>>>>>>>>>
> > >> >>>>>>>>>>     rule ssd {
> > >> >>>>>>>>>>             ruleset 1
> > >> >>>>>>>>>>             type replicated
> > >> >>>>>>>>>>             min_size 1
> > >> >>>>>>>>>>             max_size 10
> > >> >>>>>>>>>>             device class = ssd
> > >> >>>>>>>>>
> > >> >>>>>>>>> Would that be sane?
> > >> >>>>>>>>>
> > >> >>>>>>>>> Why not:
> > >> >>>>>>>>>
> > >> >>>>>>>>> step set-class ssd
> > >> >>>>>>>>> step take default
> > >> >>>>>>>>> step chooseleaf firstn 0 type host
> > >> >>>>>>>>> step emit
> > >> >>>>>>>>>
> > >> >>>>>>>>> Since it's a 'step' you take, am I right?
> > >> >>>>>>>>
> > >> >>>>>>>> Good idea... a step is a cleaner way to extend the
> syntax!
> > >> >>>>>>>>
> > >> >>>>>>>> sage
> > >> >>>>>>>> --
> > >> >>>>>>>> To unsubscribe from this list: send the line
> "unsubscribe ceph-devel" in
> > >> >>>>>>>> the body of a message to majordomo@vger.kernel.org
> > >> >>>>>>>> More majordomo info at 
> http://vger.kernel.org/majordomo-info.html
> > >> >>>>>>>>
> > >> >>>>>>>
> > >> >>>>>>> --
> > >> >>>>>>> Loïc Dachary, Artisan Logiciel Libre
> > >> >>>>>>> --
> > >> >>>>>>> To unsubscribe from this list: send the line "unsubscribe
> ceph-devel" in
> > >> >>>>>>> the body of a message to majordomo@vger.kernel.org
> > >> >>>>>>> More majordomo info at 
> http://vger.kernel.org/majordomo-info.html
> > >> >>>>>>>
> > >> >>>>>
> > >> >>>>> --
> > >> >>>>> Loïc Dachary, Artisan Logiciel Libre
> > >> >>>>> --
> > >> >>>>> To unsubscribe from this list: send the line "unsubscribe
> ceph-devel" in
> > >> >>>>> the body of a message to majordomo@vger.kernel.org
> > >> >>>>> More majordomo info at 
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> > >> >>>>
> > >> >>>
> > >> >>> --
> > >> >>> Loïc Dachary, Artisan Logiciel Libre
> > >> >>
> > >> >
> > >> > --
> > >> > Loïc Dachary, Artisan Logiciel Libre
> > >> > --
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> >
> 
> 
>