Am 27.05.2012 13:33, schrieb Alexandre DERUMIER:
how much time to flush from journal to disks ?
I don't know how to measure this.
Do an iostat, you must see timelapse of write inactivity on disk (datas are written to journal) , then after a timelapse
> of write activity on disk.(data flushed from journal to disk)
No it always starts in parallel. Journal is set to 1GB. I've now moved
the journal to disk - so i can use iostat.
As ceph starts to write to journal and
disk in parallel
this is strange, from doc:
http://ceph.com/wiki/OSD_journal
the journal mode should be write-ahead with xfs.
So write to journal first then flush to disk each 30sec.
I'm not quite sure as:
http://ceph.com/wiki/Ceph.conf#filestore_journal_writeahead
says there are two options:
filestore journal writeahead
and
filestore journal parallel
but even
filestore journal writeahead = 1
filestore journal parallel = 0
results in a parallel start.
maybe your tmpfs is too small, and flushs occurs at 50% of free space on journal.
If by exemple, your flush occurs each 1 or 2seconds, this can cause very slow write.
1GB? My 1Gbit/s LAN test connection can't handle more than about
120MB/s. So there's at least room for 8-10s.
;-(
Stefan
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