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> The time variation is caused cache coherence. when client has valid information > in its cache, 'stat' operation will be fast. Otherwise the client need to send > request to MDS and wait for reply, which will be slow. This sounds like the behavior I had with CephFS giving me question marks. When I had a directory with a large amount of files in it and the first ls -la took a while to populate and ended with some unknown stats. The second time I did an ls -la it ran quick with no question marks. My inquiry was if there is a timeout that could occur? since it has to go ask the mds on a different machine it seems plausible that the full response is not coming back in time or fails to get all stats at some point. I could test this more; is there a command or proccess I can perform to flush the ceph-fuse cache? Thanks, Scott On Fri, Mar 13, 2015 at 1:49 PM Francois Lafont <[email protected]> wrote: > Hi, > > Yan, Zheng wrote : > > >> http://tracker.ceph.com/issues/11059 > >> > > > > It's a bug in ACL code, I have updated http://tracker.ceph.com/ > issues/11059 > > Ok, thanks. I have seen and I will answer quickly. ;) > > >> I'm still surprised by such times. For instance, It seems to me > >> that, with a mounted nfs share, commands like "ls -la" are very > >> fast in comparison (with a directory which contains the same number > >> of files). Can anyone explain to me why there is a such difference > >> between the nfs case and the cephfs case? This is absolutely not a > >> criticism but it's just to understand the concepts that come into > >> play. In the case of "ls -al" ie just reading (it is assumed that > >> there is no writing on the directory), the nfs and the cephfs cases > >> seem to me very similar: the client just requests a stat on each file > >> in the directory. Am I wrong? > > > > NFS has no cache coherence mechanism. It can't guarantee one client > always > > see other client's change. > > Ah ok, I didn't know that. Indeed, now I understand that can generate > performance impact. > > > The time variation is caused cache coherence. when client has valid > information > > in its cache, 'stat' operation will be fast. Otherwise the client need > to send > > request to MDS and wait for reply, which will be slow. > > Ok, thanks a lot for your explanations. > Regards. > > -- > François Lafont > _______________________________________________ > ceph-users mailing list > [email protected] > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >
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