Relationship to parameter memory-size and filesize

Operations Configuration
1

I’m using Aerospike In-Memory + HDD disk Persistence.

What’s the relationship to parameter memory-size and filesize in aerospike.conf? Shall they be equal or filesize > memory-size? (Any formula for it?) (Assume only one data file used)

namespace test {
        replication-factor 2
        memory-size 50G
        default-ttl 0 # Never expire/evict.
        ldt-enabled true

        storage-engine device {
               file /aerospike/data/test.dat
               filesize 64G
               data-in-memory true # Store data in memory in addition to file.
        }
}
2

We have some good formulas in the capacity planning page explaining overheads and memory:

http://www.aerospike.com/docs/operations/plan/capacity/

As a rule of Thumb for data in-memory with Persistence on Disk:

Filesize = 2 x (Memory Size)

Remember that each record with have an overhead of 64 bytes in memory for the primary index.

and 128k on disk (default write block size)