Post by ***@yahoo.com [hercules-390]
Thanks Peter, I was arriving to the same conclusion, but not clear how
to use it.
I understand I need to change my config and add an sf= template for
each volume, but not sure how to use it for my goal.
-take a synchronized snapshot of all the volumes without stopping emulator
- be able to go back to a specific snapshot, possibily without
stopping the emulator
Would it be possible? If so, how would you orchestrate it?
Thx a lot
The idea is as follows :
- have shadow files configured.... sf= in the DASD statement.
before doing your backup :
- stopall (This will freeze hercules for a very short time)
- sf+* (this is a VERY quick operation since it only involves creating
stub files and turning the base files read only)
- startall (hercules resumes execution)
** Backup the base disks - they will no longer be touched and indicate a
consistent image at the time of the 'stopall' since all modifications
are now going to the shadow files.
After backup is done :
sf-* (no need to stop anything at this point.. The shadow files will be
commited back to the base files on the fly and deleted when the
operation is done) - this MAY take some time depending on the size of
the DASDs and the amount of activity that occured during the backup
phase. so maybe expect a slight performance degradation on the I/O side
for a little while.)
sfc* (optional - performs garbage colllection and recompression if
If you restore the DASDs, and re-ipl your system from there it will
appear as if a complete power failure had occured (with the necessary
EPO) at the time of the "stopall" command.
This works for ANY operating system running under hercules... Not only MVS !
You may also chose to do a primary backup of the base files... and then
to only backup shadow files.. base and shadow files are hierarchical..
so if can do step 1 for the initial backup (and not the sf-*)... then do
step 1 again for subsequent backups and only backup the level 1 shadow
files afterwards... And if you're crazy enough, use git for versioning
and now you have an incremental forever backup system !
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