Question

SQL Server uses .mdf for data files and .ldf for log files, but what are .ndf files?

What are the benefits of these files?

Answer 1

From Files and Filegroups Architecture

Secondary data files

Secondary data files make up all the data files, other than the primary data file. Some databases may not have any secondary data files, while others have several secondary data files. The recommended file name extension for secondary data files is .ndf.

Also from file extension NDF – Microsoft SQL Server secondary data file

See Understanding Files and Filegroups

Secondary data files are optional, are
user-defined, and store user data.
Secondary files can be used to spread
data across multiple disks by putting
each file on a different disk drive.
Additionally, if a database exceeds
the maximum size for a single Windows
file, you can use secondary data files
so the database can continue to grow.

The recommended file name extension
for secondary data files is .ndf.

/

For example, three files, Data1.ndf,
Data2.ndf, and Data3.ndf, can be
created on three disk drives,
respectively, and assigned to the
filegroup fgroup1. A table can then be
created specifically on the filegroup
fgroup1. Queries for data from the
table will be spread across the three
disks; this will improve performance.
The same performance improvement can
be accomplished by using a single file
created on a RAID (redundant array of
independent disks) stripe set.
However, files and filegroups let you
easily add new files to new disks.