Hello Ceph Users,
I am finding that the write latency across my ceph clusters isn't great and I
wanted to see what other people are getting for op_w_latency. Generally I am
getting 70-110ms latency.
I am using: ceph --admin-daemon /var/run/ceph/ceph-osd.102.asok perf dump |
grep -A3 '\"op_w_latency' | grep 'avgtime'
Ram, CPU and network don't seem to be the bottleneck. The drives are behind a
dell H810p raid card with a 1GB writeback cache and battery. I have tried with
LSI JBOD cards and haven't found it faster ( as you would expect with write
cache ). The disks through iostat -xyz 1 show 10-30% usage with general service
+ write latency around 3-4ms. Queue depth is normally less than one. RocksDB
write latency is around 0.6ms, read 1-2ms. Usage is RBD backend for Cloudstack.
Dumping the ops seems to show the latency here: (ceph --admin-daemon
/var/run/ceph/ceph-osd.102.asok dump_historic_ops_by_duration |less)
{
"time": "2019-04-01 22:24:38.432000",
"event": "queued_for_pg"
},
{
"time": "2019-04-01 22:24:38.438691",
"event": "reached_pg"
},
{
"time": "2019-04-01 22:24:38.438740",
"event": "started"
},
{
"time": "2019-04-01 22:24:38.727820",
"event": "sub_op_started"
},
{
"time": "2019-04-01 22:24:38.728448",
"event": "sub_op_committed"
},
{
"time": "2019-04-01 22:24:39.129175",
"event": "commit_sent"
},
{
"time": "2019-04-01 22:24:39.129231",
"event": "done"
}
]
}
}
This write was around a very slow one and I am wondering if I have a few ops
that are taking along time and most that are good....
What else can I do to figure out where the issue is?
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