On Tue, Aug 4, 2015 at 12:42 PM, Goncalo Borges <goncalo@xxxxxxxxxxxxxxxxxxx> wrote: > Hi Yan Zheng > > >> >> >> >> Now my questions: >> >> 1) I performed all of this testing to understand what would be the minimum >> size (reported by df) of a file of 1 char and I am still not able to find >> a >> clear answer. In a regular posix file system, the size of a 1 char (1 >> byte) >> file is actually constrained by the filesystem block size. A 1 char file >> would occupy 4 KB in a filesystem configured with a 4 KB blocksize. In >> ceph >> / cephfs I would expect that a 1 char file would be constrained by the >> Object size x Number of replicas. However, I was not able to understand >> the >> numbers I was getting and that was why I started to dig on this topic. Can >> you actually also clarify this question? >> >> rbytes is sum of sizes of file under the directory, nothing do with >> block size. If there are sparse files, rbytes of root directory can be >> larger then used space of FS, > > > Maybe I did not explain myself clearly. I am not saying that block size has > something to do with rbytes, I was just making a comparison with what I > expect in a regular POSIX filesystem. Let me put the question in the > following / different way: > > 1) I know that, if I only have one char file in a ext4 filesystem, where my > filesystem was set with a 4KB blocksize, a df would show 4KB as used space. > > 2) now imagine that I only have one char file in my Cephfs filesystem, and > the layout of my file is object_size=512K, stripe_count=2, and > stripe_unit=256K. Also assume that I have set my cluster to have 3 > replicates. What would be the used space reported by a df command in this > case? > > My naive assumption would be that a df should show as used space 512KB x 3. > Is this correct? No. Used space reported by df is the sum of used space of OSDs' local store. A 512k file require 3x512k space for data, OSD and local filesystem also need extra space for tracking these data. > > > Cheers > Goncalo > > -- > Goncalo Borges > Research Computing > ARC Centre of Excellence for Particle Physics at the Terascale > School of Physics A28 | University of Sydney, NSW 2006 > T: +61 2 93511937 > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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