Names of migrated data sets

When DFSMShsm migrates a data set, it changes the catalog entry for that data set. The data set retains its name, so the users of the data set know how to address it, but the location is changed to MIGRAT. However, DFSMShsm gives the migration copy of the data set a name of the form:

prefix.HMIG.Tssmmhh.user1.user2.Xyddd

If patch-enabled, the following dataset name will be generated:

prefix.HMIG.Tcccchh.user1.user2.Xyddd

where:

prefix is the prefix you specify with the SETSYS MIGRATEPREFIX command.
HMIG and T are constants.
Note: If two or more data sets with the same first two high-level qualifiers are migrated during the same second on the same day, DFSMShsm assigns a letter other than T to one of these data sets.
ssmmhh is the 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 is 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 and user2 are the first two qualifiers of the data set name.
Xyddd is the year and day. X is replaced with a letter that represents the decade as follows:
G = 1970 B = 2020

H = 1980 C = 2030

I = 1990 D = 2040

J = 2000 E = 2050

A = 2010 F = 2060

If, for example, I9012 replaces Xyddd, then I9012 represents January 12, 1999.

If you need to access a single-file format tape, you must specify a valid data set name for the single file that comprises up to 255 tape volumes. The following migrated data set name is valid for each set of cartridge-type tape volumes in single-file format:

prefix.HMIGTAPE.DATASET

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

The following tape data set name for each copy of a cartridge-type tape volume is created by the TAPECOPY command or the duplex tape option:

prefix.COPY.HMIGTAPE.DATASET