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. 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 -- 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
