Why mongodb arbiter needs dbpath? - mongodb

Question

An mongodb arbiter roles are as follows:
An arbiter does not have a copy of data set and cannot become a primary. However, an arbiter participates in elections for primary. An arbiter has exactly 1 election vote.
Arbiters are mongod instances that are part of a replica set but do not hold data. Then, why arbiter needs dbpath?

Answer 1

The arbiter stores various housekeeping data, which you can inspect by looking at the local database:
MongoDB Enterprise ruby-driver-rs:ARBITER> db.getMongo().setSlaveOk()
MongoDB Enterprise ruby-driver-rs:ARBITER> use local
switched to db local
MongoDB Enterprise ruby-driver-rs:ARBITER> db.runCommand({listCollections:1})
{
"cursor" : {
"id" : NumberLong(0),
"ns" : "local.$cmd.listCollections",
"firstBatch" : [
{
"name" : "system.replset",
"type" : "collection",
"options" : {
},
"info" : {
"readOnly" : false,
"uuid" : UUID("108fbabe-4139-4d3d-8326-fc8e169b811d")
},
"idIndex" : {
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
}
},
{
"name" : "startup_log",
"type" : "collection",
"options" : {
"capped" : true,
"size" : 10485760
},
"info" : {
"readOnly" : false,
"uuid" : UUID("1c3ed741-a7f8-4fad-89f9-36f979cbfa22")
},
"idIndex" : {
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
}
},
{
"name" : "replset.oplogTruncateAfterPoint",
"type" : "collection",
"options" : {
},
"info" : {
"readOnly" : false,
"uuid" : UUID("37c4d64b-8fcc-4aa5-b1e0-2ac6b71e893a")
},
"idIndex" : {
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
}
},
{
"name" : "replset.election",
"type" : "collection",
"options" : {
},
"info" : {
"readOnly" : false,
"uuid" : UUID("53fc68a9-19c9-4262-b152-fafa99ea55f5")
},
"idIndex" : {
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
}
},
{
"name" : "replset.minvalid",
"type" : "collection",
"options" : {
},
"info" : {
"readOnly" : false,
"uuid" : UUID("5564332b-3c3f-4103-acbd-c53c7a71581c")
},
"idIndex" : {
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
}
},
{
"name" : "system.rollback.id",
"type" : "collection",
"options" : {
},
"info" : {
"readOnly" : false,
"uuid" : UUID("fa26f83a-8843-4b6d-8d4d-4cde192976bd")
},
"idIndex" : {
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "_id_"
}
}
]
},
"ok" : 1
}