When CRUSH algorithm detects, that an object cannot be placed in a PG that came through the draw, does CRUSH not draw another PG, until the PG drawn can be written to? On Mon, Mar 27, 2017 at 2:34 PM, kefu chai <tchaikov@xxxxxxxxx> wrote: > On Fri, Mar 24, 2017 at 8:08 PM, Spandan Kumar Sahu > <spandankumarsahu@xxxxxxxxx> wrote: >> I understand that, we can't write to objects which belong to the >> particular PG (the one having at least one full OSD). But a storage >> pool can have multiple PGs, and some of them must have only non-full >> OSDs. Through those PGs, we can write to the OSDs which are not full. > > but we cannot impose the restriction on the client that only a subset > of PGs of the given pool can be written. > >> >> Did I understand it correctly? >> >> >> On Fri, Mar 24, 2017 at 1:01 PM, kefu chai <tchaikov@xxxxxxxxx> wrote: >>> Hi Spandan, >>> >>> Please do not email me privately, instead use the public mailing list, >>> which allows other developers to provide you help if I am unable to do >>> so. it also means that you can start interacting with the rest of the >>> community instead of only me (barely useful). >>> >>> On Fri, Mar 24, 2017 at 2:38 PM, Spandan Kumar Sahu >>> <spandankumarsahu@xxxxxxxxx> wrote: >>>> Hi >>>> >>>> I couldn't figure out, why is this happening, >>>> >>>> "...Because once any of the storage device assigned to a storage pool is >>>> full, the whole pool is not writeable anymore, even there is abundant space >>>> in other devices." >>>> -- Ceph GSoC Project Ideas (Smarter reweight-by-utilisation) >>>> >>>> I went through this[1] paper on CRUSH, and according to what I understand, >>>> CRUSH pseudo-randomly chooses a device based on weights which can reflect >>>> various parameters like the amount of space available. >>> >>> CRUSH is a variant of consistent hashing. Ceph cannot automatically >>> choose *another* OSD which is not chosen by CRUSH, even if that OSD is >>> not full and has abundant space. >>> >>>> >>>> What I don't understand is, how will it stop a pool having abundant space on >>>> other devices, from getting selected, if one of its devices is full? Sure, >>>> the chances of getting selected might decrease, if one device is full, but >>>> how does it completely prevent writing to the pool? >>> >>> if a PG are served by three OSDs. if any of them is full, how can we >>> continue creating/writing to objects which belong to that PG? >>> >>> >>> -- >>> Regards >>> Kefu Chai >> >> >> >> -- >> Spandan Kumar Sahu >> IIT Kharagpur > > > > -- > Regards > Kefu Chai -- Spandan Kumar Sahu IIT Kharagpur -- 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
