Aerospike default.dat file is huge for no reason - aerospike

Question

I have a running Aerospike server with about 36,000 records in a single set. All I'm storing is a few bins for the set. I have configured my aerospike.conf file to persist data on disk as well:
namespace default {
replication-factor 2
memory-size 4G
default-ttl 0
storage-engine device {
file /opt/aerospike/data/default.dat
filesize 2T
data-in-memory true
}
}
The problem I'm having is that my /opt/aerospike/data/default.dat file is listed in my system as about 2TB:
/opt/aerospike/data# ls -lh
total 10M
-rw------- 1 root root 2.0T Jun 5 19:01 default.dat
My questions are:
Why does this .dat file have to be 2TB when the data I'm using in Aerospike is minimal for now?
My hard drive limit is 78GB, so why isn't my Ubuntu system not giving me out of drive space errors?
System disk space looks fine:
df -h --total
Filesystem Size Used Avail Use% Mounted on
/dev/xvda1 79G 4.2G 72G 6% /
none 4.0K 0 4.0K 0% /sys/fs/cgroup
udev 2.0G 8.0K 2.0G 1% /dev
tmpfs 395M 424K 395M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 2.0G 0 2.0G 0% /run/shm
none 100M 0 100M 0% /run/user
total 83G 4.2G 76G 6% -
Anyone have any ideas?

Answer 1

Well,
Aerospike uses sparse file (or kind of) for storing its file storage.
So when you specified the filesize 2T in namespace config, Aerospike will create a sparse file of size 2TB that you are seeing.
http://en.wikipedia.org/wiki/Sparse_file
So, its just a file with some metadata and not real 2TB data. Once the file content has actually filled your disk, you will see the usual disk full errors on both your system as well as in Aerospike.