Hi, We observe that we can easily create slow requests with a simple dd on CephFS:
--> [root@p05153026953834 dd]# dd if=/dev/zero of=xxx bs=4M count=1000 1000+0 records in 1000+0 records out 4194304000 bytes (4.2 GB) copied, 4.27824 s, 980 MB/s ceph -w: 2014-01-31 14:28:44.009543 osd.450 [WRN] 1 slow requests, 1 included below; oldest blocked for > 31.088950 secs 2014-01-31 14:28:44.009676 osd.450 [WRN] slow request 31.088950 seconds old, received at 2014-01-31 14:28:12.920423: osd_op(client.16735018.1:22493091 100000352b3.000002e9 [write 0~4194304,startsync 0~0] 0.518f2eef snapc 1=[] e32400) v4 currently waiting for subops from [87,1190] <--- From what we see, the OSDs are not busy, so we suspect that it is the client starting all requests, but then the requests take longer than 30 secs to finish writing, i.e. flushing the client-side buffers. Is our understanding correct? Do these slow requests have an impact on requests from other clients, i.e. some OSD resources consumed by these clients? The setup is: Client: kernel 3.13.0, 1GbE MDS Emperor 0.72.2 OSDs Dumpling 0.67.5 Thanks! Dan & Arne -- Arne Wiebalck CERN IT
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