Hi huang jun,
Thanks for your reply.
Still now, I am really confused...
According to your reply, ceph's journal operates as a full journal(meaning
metadata and object data).
Is that right?
I tested for jounral I/O through rados bench and trace the journal I/O from
blktrace.
[client node]
root@ceph-mon01:~# rados -p rados-test df
pool name KB objects clones degraded
unfound rd rd KB wr B
rados-test *528384* 129 0 258
0 0 0 129 4
total used 658876 129
total avail 156547604
total space 157206480
[osd node - blktracte output]
CPU0 (8,16):
Reads Queued: 0, 0KiB Writes Queued: 821,
551804KiB
Read Dispatches: 0, 0KiB Write Dispatches: 588,
529428KiB
Reads Requeued: 0 Writes Requeued: 0
Reads Completed: 0, 0KiB Writes Completed: 704,
*529428KiB*
Read Merges: 0, 0KiB Write Merges: 117,
6144KiB
Read depth: 0 Write depth: 32
IO unplugs: 117 Timer unplugs: 0
The result also seems to says that the full data are written to journal.
However, the ceph documentation says,
*Consistency:* Ceph OSD Daemons require a filesystem interface that
guarantees atomic compound operations.
Ceph OSD Daemons *write a description of the operation to the journal*
and *apply
the operation to the filesystem*
How can I understand above document?
I will really appreciate for your help.
Thanks.
2016-09-01 19:09 GMT+09:00 huang jun <[email protected]>:
> 2016-09-01 17:25 GMT+08:00 한승진 <[email protected]>:
> > Hi all.
> >
> > I'm very confused about ceph journal system
> >
> > Some people said ceph journal system works like linux journal filesystem.
> >
> > Also some people said all data are written journal first and then
> written to
> > OSD data.
> >
> > Journal of Ceph storage also write just metadata of object or write all
> data
> > of object?
> >
> > Which is right?
> >
>
> data writen to osd first will write to osd journal through dio, and
> then submit to objectstore,
> that will improve the small file write performance bc the journal
> write is sequential not random,
> and journal can recover the data that written to journal but didn't
> write to objectstore yet, like outage..
>
> > Thanks for your help
> >
> > Best regards.
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > ceph-users mailing list
> > [email protected]
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> >
>
>
>
> --
> Thank you!
> HuangJun
>
_______________________________________________
ceph-users mailing list
[email protected]
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
