The VSAM datasets are divided into three types based on the storage of data and accessing of data. They are -

  1. Entry Sequential Dataset (ESDS) .
  2. Key Sequential Dataset (KSDS) .
  3. Relative Record Dataset .
    1. Fixed-length RRDS (RRDS).
    2. Variable-length RRDS (VRRDS).
  4. Linear Dataset (LDS) .

VSAM file types supporting access modes and record length -

File Organization Access Type Record Length
Sequential Access Random Access Dynamic Access Fixed-length Variable-length
ESDS Yes No No Yes Yes
KSDS Yes Yes Yes Yes Yes
RRDS Yes Yes Yes Yes Yes

ESDS, KSDS, RRDS, VRRDS, and LDS Comparison -

ESDS KSDS Fixed-length RRDS Variable-length RRDS LDS
What is the method for sequential access? Entry/Inserting order Primary key field ascending order RRN order RRN order No record level processing
What are the types of record format? Allows fixed-length, variable-length and spanned records Allows fixed-length, variable-length and spanned records Allows fixed-length Allows variable-length No record level processing
What is the method for direct access? RBA Key or RBA RRN RRN Acess with DIV(Data-In-Virtual)
What are the Components the dataset have? DATA Component only DATA and INDEX Components DATA Component only DATA and INDEX Components DATA Component only
Can RBA or RRN change? A records's RBA can't change A records's RBA can change A records's RRN can't change A records's RRN can't change No record level processing
Can we delete the record? Record can't be deleted. We can reuse the record for a record of the same length. Deleting the record space becomes free space. Slot freeed by deleting the record can be reused. Deleting the record space becomes free space. No record level processing
Can we reuse the deleted record space? No Yes Yes Yes No record level processing
Is record length changeable? No Yes No Yes Extended format allowed
Where are new records added? End of the file Anywhere RRN Slot RRN Slot CI
Can you REUSE the file? Yes (If no AIX) Yes (If no AIX) Yes Yes Yes
Can we access the data set through an alternate index? Yes Yes No No No
What space used to insert records? Space at the end of the dataset used Free space is used for inserting and lengthening records Empty slots are used Free space is used for inserting and lengthening records No record level processing
Is embedded free space defined? No Yes No No No
Was spanned Records allowed? Allowed Allowed No spanned records No spanned records No spanned records
Was Extended Format/Compression allowed? Extended format allowed Extended format or compression allowed Extended format allowed Extended format allowed Extended format allowed