sizing storage for 100 M files

Hi,

We plan to acquire some storage for our storage system to be based on 
iRODS + PostgreSQL. iRODS uses PostgreSQL to store the metadata of a 
file. For each file that iRODS stores, a row is added to each of the 
following tables in PostgreSQL.

create table R_DATA_MAIN
(
  data_id bigint not null,
  coll_id bigint not null,
  data_name varchar(1000) not null,
  data_repl_num INTEGER not null,
  data_version varchar(250) DEFAULT '0',
  data_type_name varchar(250) not null,
  data_size bigint not null,
  resc_group_name varchar(250),
  resc_name varchar(250) not null,
  data_path varchar(2700) not null,
  data_owner_name varchar(250) not null,
  data_owner_zone varchar(250) not null,
  data_is_dirty INTEGER DEFAULT 0,
  data_status varchar(250),
  data_checksum varchar(1000),
  data_expiry_ts varchar(32),
  data_map_id bigint DEFAULT 0,
  data_mode varchar(32),
  r_comment varchar(1000),
  create_ts varchar(32),
  modify_ts varchar(32)
);

And:

create table R_OBJT_ACCESS
(
  object_id bigint not null,
  user_id bigint not null,
  access_type_id bigint not null,
  create_ts varchar(32),
  modify_ts varchar(32)
);

Size of R_DATA_MAIN ~= 7618 bytes
Size of R_OBJT_ACCESS ~= 88 bytes

According to the PostgreSQL FAQ, a PostgreSQL database may require up to 
five times the disk space to store data from a text file.

Is it valid for me to use this multiplier to estimate the storage 
requirement for 100 M files?
i.e. estimated storage = (7618 bytes + 88 bytes) * 100 M * 5
                      = 3.853 TB

Thank you in advance for your help.

Alinga