On 02-11-15 11:56, Jan Schermer wrote: > Can those hints be disabled somehow? I was battling XFS preallocation > the other day, and the mount option didn't make any difference - maybe > because those hints have precedence (which could mean they aren't > working as they should), maybe not. >
This config option? OPTION(rbd_enable_alloc_hint, OPT_BOOL, true) // when writing a object, it will issue a hint to osd backend to indicate the expected size object need Found in src/common/config_opts.h Wido > In particular, when you fallocate a file, some number of blocks will be > reserved without actually allocating the blocks. When you then dirty a > block with write and flush, metadata needs to be written (in journal, > synchronously) <- this is slow with all drives, and extremely slow with > sh*tty drives (doing benchmark on such a file will yield just 100 write > IOPs, but when you allocate the file previously with dd if=/dev/zero it > will have 6000 IOPs!) - and there doesn't seem to be a way to disable it > in XFS. Not sure if hints should help or if they are actually causing > the problem (I am not clear on whether they preallocate metadata blocks > or just block count). Ext4 does the same thing. > > Might be worth looking into? > > Jan > > >> On 31 Oct 2015, at 19:36, Gregory Farnum <gfar...@redhat.com >> <mailto:gfar...@redhat.com>> wrote: >> >> On Friday, October 30, 2015, mad Engineer <themadengin...@gmail.com >> <mailto:themadengin...@gmail.com>> wrote: >> >> i am learning ceph,block storage and read that each object size is >> 4 Mb.I am not clear about the concepts of object storage still >> what will happen if the actual size of data written to block is >> less than 4 Mb lets say 1 Mb.Will it still create object with 4 mb >> size and keep the rest of the space free and unusable? >> >> >> No, it will only take up as much space as you write (plus some >> metadata). Although I think RBD passes down io hints suggesting the >> object's final size will be 4MB so that the underlying storage (eg >> xfs) can prevent fragmentation. >> -Greg >> _______________________________________________ >> ceph-users mailing list >> ceph-users@lists.ceph.com <mailto:ceph-users@lists.ceph.com> >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
