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I'm using MongoDB 2.4, and when I start the mongo for the 1st time, I get a 9GB of journaling files on one server, and on the second server I get only 0.5GB of files for journaling. On the first server, MongoDB take 5 minutes to load! and on the second one it takes a few seconds. Both instances have no data and running for the 1st time. Each server works independently and both of them are not related. Each server have it's own shards (all shards - 3 of them, are in the same server).

Which means for each server I have:

/usr/mongodb/bin/mongod --configsvr --dbpath /data/svr1 --port 27019

/usr/mongodb/bin/mongod --configsvr --dbpath /data/svr2 --port 27020

/usr/mongodb/bin/mongod --configsvr --dbpath /data/svr3 --port 27021

/usr/mongodb/bin/mongod --dbpath /data/db1 --port 27010

/usr/mongodb/bin/mongod --dbpath /data/db2 --port 27011

/usr/mongodb/bin/mongod --dbpath /data/db3 --port 27012

/usr/mongodb/bin/mongos --configdb localhost:27019,localhost:27020,localhost:27021

and the script that creates the shards:

sh.addShard("localhost:27010");

sh.addShard("localhost:27011");

sh.addShard("localhost:27012");

sh.enableSharding("somescheme");

I wondered why I get a 9GB files for journaling on the 1st one and 0.5GB on the second? The 1st one have a bigger hard disk and its not SSD, the second is SSD and smaller. any ideas? Thanks!!!

Elad Kolberg
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    Are you running with the smallfiles flag (either command line or in your .cfg) on your second host? When enabled this reduces the size allocated for journal and data files. Another thing to note is MongoDB will only preallocate journal files if your mongod instances decides it would be more efficient to do so then building on the fly. See this for more info: http://docs.mongodb.org/manual/core/journaling/#journal-files – James Wahlin Jun 18 '13 at 12:47
  • nope, not running with smallfiles conf on both of them. I read that it's not recommended to run with smallfiles when you have a large amount of data on each node, only if you have a lot of nodes with small amount of data for each. – Elad Kolberg Jun 18 '13 at 12:53
  • The is right, the only case I have seen for smallfiles in production is when you are running a large # of small databases. Can you provide an ls -l on both journal directories? Would be interesting to see the size and # of files. – James Wahlin Jun 18 '13 at 13:01

1 Answers1

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MongoDB will pre-allocate journal files if it decides that it's better to do so. Check your logs for something like this:

Thu Mar 10 20:49:33 [initandlisten] preallocating a journal file db/journal/prealloc.0
Thu Mar 10 20:52:49 [initandlisten] preallocating a journal file db/journal/prealloc.1
John Feibusch
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