Re: Firefly, cephfs issues: different unix rights depending on the client and ls are slow

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On Sat, Mar 14, 2015 at 7:03 AM, Scottix <scottix@xxxxxxxxx> wrote:
> ...
>
>
>> 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.

unknown stats shouldn't happen. which kernel are ypu using? can you reproduce
it with ceph-fuse?

Regards
Yan, Zheng

>
> 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 <flafdivers@xxxxxxx> 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
>> ceph-users@xxxxxxxxxxxxxx
>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>
>
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