Hi Andreas, Andreas Dilger wrote: > On Jul 27, 2009 14:24 +0200, Thomas Roth wrote: >> I'm copying around data between 2 MDTs in a test system. Having mounted >> the partitione as 'ldiskfs', I had a look in MDT/ROOT. I found all my >> test data there, but I'm puzzled by the indicated file sizes. For >> example I had put one of my holiday's movies, it's 40MB. On the >> ldiskfs-mounted MDT, I find a corresponding entry, which also has 40MB, >> as given by 'ls -lh'. Of course, the latter file doesn't have the >> contents of that movie, but why is it the same size? 'ls -li' also gives >> identical results, btw. >> On the other hand, there is another movie which is .6.4MB as such, but >> 0B on the MDT partition. > > In Lustre 1.6.7 the "approximate" file size started to be stored on the > MDT inodes in order to facilitate[*] filesystem backup utilities to > allow them to have a fast estimate of the file size w/o having to access > the OST objects (that hold the authoritative size). This size cannot > be used as the official file size in 1.x because there isn't sufficient > locking and recovery of the size in case of a crash, though a preview of > this feature (Size On MDS, SOM) will be available in the 2.0 release.
I get the impression that this feature hampers the device level backup - or is it file level backup: Extracting extended attributes and make a tar archive of the MDT: the latter step now takes 5 days on our production system (which is 1.6.7.1). And right now I'm trying to do a rsync - copy of that MDT. When that seemed to be stuck with a particular, I checked the file, on the source, albeit primitively with "ls -lh". That told me that the file was 9.1GB, and the rsync behaves just as you would expect when it has to transfer 9GB over the network - takes some time. In fact, there are several of these files, and as I mentioned, the MDT takes only 13GB on disk, so all of this is a bit confusing. The first attempts to copy the MDT resulted immediately in a target file system blown up beyond proportions. I have since added the options "--sparse" to my rsync command line. Now the target system seems to keep small, but I have yet to see if the result could be used as an MDT at all. Of course all this may just be due to our MDT being damaged somehow ... >> Both movies play nicely, so there is no problem with this file system. >> On our production system, the MDT takes 13GB for 250TB of data, >> obviously there aren't entries on the MDT taking the size of the real >> data files ;-) >> >> So my question is whether the file size reported by 'ls' on the MDT as >> any practical implication? > > This size is not actively updated for pre-existing files, nor is it > always guaranteed to be written in case of a crash, which is why you > see some (likely older) files that do not have the size information. > > Cheers, Andreas > -- > Andreas Dilger > Sr. Staff Engineer, Lustre Group > Sun Microsystems of Canada, Inc. > Regards, Thomas _______________________________________________ Lustre-discuss mailing list [email protected] http://lists.lustre.org/mailman/listinfo/lustre-discuss
