Generating names of backup versions of data sets

prefix.BACK.Tssmmhh.user1.user2.Xyddd

prefix.BACK.Tcccchh.user1.user2.Xyddd

where:

prefix

Prefix you specify with the SETSYS BACKUPPREFIX command.

BACK

T

Constants.

Note: If two data sets with the same first two high-level qualifiers are backed up at the same second on the same day, DFSMShsm assigns a letter other than T to one of these data sets.

ssmmhh

Time in seconds, minutes, and hours.

If the format is Tcccchh, then cccchh is the time in hundredths of seconds from the beginning of the hour converted to four alphabetic characters, and hh is hours.

The four characters cccc may be converted to time as follows:

1. Create a variable for each character of the string cccc, using p1 through p4, from left to right. Then assign a value 0 thru 24 for each character A thru Y in the sequence. (Note that 25 characters are used, for A through Y, but not Z.)
2. Find the total hundredths of seconds from the beginning of the hour using this formula:

   hunds_seconds_begin_hour = p1+(p2*25)+(p3*625)+(p4*625*25)

3. Find the minutes, seconds, and hundredths using these formulae (% = integer division):

   minutes = hunds_seconds_begin_hour%(60*100)
   seconds = (hunds_seconds_begin_hour-minutes*60*100)%100
   hundredths = hunds_seconds_begin_hour-minutes*60*100-seconds*100

cccchh

The time in hundredths of seconds from the beginning of the hour converted to four alphabetic characters (cccc) and hours (hh).

The four characters cccc may be converted to time as follows:

1. Create a variable for each character of the string cccc. Assume these variables are p1 thru p4, from left to right. Assign a value 0 thru 24 for each character A thru Y, in sequence (25 characters are used A - Y, but not Z).
2. Find the total seconds from the beginning of the hour:

   hunds_seconds_begin_hour = p1+(p2*25)+(p3*625)+(p4*625*25)

3. Find minutes, seconds, and hundredths (% = integer division):

   minutes = hunds_seconds_begin_hour%(60*100)    
   seconds = (hunds_seconds_begin_hour-minutes*60*100)%100  
   hundredths = hunds_seconds_begin_hour-minutes*60*100-seconds*100 

For more information, refer to "Changing DFSMShsm backup and migration generated dataset names to reduce contention for similar names and eliminating a possible performance degradation" in the "Tuning DFSMShsm" chapter of z/OS DFSMShsm Implementation and Customization Guide.

user1

user2

First two qualifiers of the data set name.

Xyddd

Decade, year, and day of the year. Valid character values for X are:

G

1970

H

1980

I

1990

J

2000

A

2010

B

2020

C

2030

D

2040

E

2050

F

2060

For example, J3032 represents February 1, 2003.

   prefix.BACKTAPE.DATASET

   prefix.COPY.BACKTAPE.DATASET

Only the last 17 characters (.BACKTAPE.DATASET) are recorded in the tape label. To access the single-file format data set, you must supply any valid first qualifier along with the .BACKTAPE.DATASET qualifiers.