I have a db named log_test1, with only 1 capped collection logs. The max size of capped collection is 512M. After I inserted 200k data, I found the disk usage of the db is 1.6G. With db.stats(), I can see the storageSize is 512M, correct, but my actual fileSize is 1.6G, why did this happen? How can I control the disk size is just my capped collection size plus index size?
> use log_test1
switched to db log_test1
> db.stats()
{
"db" : "log_test1",
"collections" : 3,
"objects" : 200018,
"avgObjSize" : 615.8577328040476,
"dataSize" : 123182632,
"storageSize" : 512008192,
"numExtents" : 3,
"indexes" : 8,
"indexSize" : 71907920,
"fileSize" : 1610612736,
"nsSizeMB" : 16,
"dataFileVersion" : {
"major" : 4,
"minor" : 5
},
"ok" : 1
}
This is probably because MongoDB preallocates data and journal files.
MongoDB 2
MongoDB 3
Taken from MongoDB Storage FAQ.