On 03/09/2012 12:39 PM, Jim Schutt wrote:
On 03/08/2012 05:26 PM, Sage Weil wrote:
On Thu, 8 Mar 2012, Jim Schutt wrote:
Hi,
I've been trying to scale up a Ceph filesystem to as big
as I have hardware for - up to 288 OSDs right now.
(I'm using commit ed0f605365e - tip of master branch from
a few days ago.)
My problem is that I cannot get a 288 OSD filesystem to go active
(that's with 1 mon and 1 MDS). Pretty quickly I start seeing
"mds e4 e4: 1/1/1 up {0=cs33=up:creating(laggy or crashed)}".
Note that as this is happening all the OSDs and the MDS are
essentially idle; only the mon is busy.
While tailing the mon log I noticed there was a periodic pause;
after adding a little more debug printing, I learned that the
pause was due to encoding pg_stat_t before writing the pg_map to disk.
Here's the result of a scaling study I did on startup time for
a freshly created filesystem. I normally run 24 OSDs/server on
these machines with no trouble, for small numbers of OSDs.
seconds from seconds from seconds to
OSD PG store() mount store() mount encode
to to all PGs pg_stat_t Notes
up:active active+clean*
48 9504 58 63 0.30
72 14256 70 89 0.65
96 19008 93 117 1.1
120 23760 132 138 1.7
144 28512 92 165 2.3
168 33264 215 218 3.2 periods of
"up:creating(laggy or crashed)"
192 38016 392 344 4.0 periods of
"up:creating(laggy or crashed)"
240 47520 1189 644 6.3 periods of
"up:creating(laggy or crashed)"
288 57024>14400>14400 9.0 never went
active;>200 OSDs out, reporting "wrongly marked me down"
Weird, pg_stat_t really shouldn't be growing quadratically. Can you look
at the size of the monitors pg/latest file, and see if those are growing
quadratically as well? I would expect it to be proportional to the
encode time.
Here's the size of the last written mon/pgmap/latest for each run,
and the time it took to encode the pg_stat_t part of that last
instance of the file:
OSDs size of pg_stat_t
latest encode
time
48 2976397 0.323052
72 4472477 0.666633
96 5969461 1.159198
120 7466021 1.738096
144 8963141 2.428229
168 10460309 3.203832
192 11956709 4.083013
240 14950445 6.453171
288 17916589 9.462052
Looks like the file size is growing linearly, but the
encode time is not?
I remembered I've been compiling with -g since I started working
with ceph (so I could poke around easily in gdb, and at small sizes
it didn't seem to hurt anything). That's how I generated the above
results.
I recompiled with -g -O2, and got this:
OSDs size of pg_stat_t
latest encode
time
48 2976461 0.052731
72 4472477 0.107187
96 5969477 0.194690
120 7466021 0.311586
144 8963141 0.465111
168 10460317 0.680222
192 11956709 0.713398
240 14950437 1.159426
288 17944413 1.714004
It seems that encoding time still isn't proportional to the
size of pgmap/latest. However, things have improved enough
that my 288 OSD filesystem goes active pretty quickly (~90 sec),
so I can continue testing at that scale.
-- Jim
And maybe send us a copy of one of the big ones?
On its way.
-- Jim
Thanks-
sage
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