RE: Where do I learn about SAN backup?

I have to disagree with some of these statements. First of all let’s agree on naming conventions of the LPARs

PRODUCTION (your live LPAR)
BACKUP (The copy made from the flash copy).

Any data which is changed on the PRODUCTION LPAR after the flash copy is not know to the BACKUP LPAR.
Any data which is changed on the BACKUP LPAR is not know by the PRODUCTION LPAR.

When talking about pointers and amount of disk used, this is all on the storage (assuming you flashed to thin provisioned LUNs). The physical amount of disk space on the SAN used by BACKUP, is directly related to the amount of data blocks which changed on PRODUCTION after the flash copy started. No data is copied between partitions.

After the flash copy has happened, you can treat these as two completely separate copies of the disks. The storage subsystem does it magic to keep track of the changes and minimize the physical amount of disk capacity used.

Another way to think about it is if PRODUCTION sees 10TB of disk capacity(WRKSYSSTS) , BACKUP will see 10TB of disk capacity(WRKSYSSTS), but the SAN may only use a total of 11TB of capacity (assuming PROD changed 1TB of data after the Flash copy).


From: Musselman, Paul<mailto:pmusselman@xxxxxxxxxxxxxxxx>
Sent: Thursday, August 24, 2017 5:15 PM
To: Midrange Systems Technical Discussion<mailto:midrange-l@xxxxxxxxxxxx>; midrange-l-bounces@xxxxxxxxxxxx<mailto:midrange-l-bounces@xxxxxxxxxxxx>
Subject: RE: Where do I learn about SAN backup?

Joe said:

Okay, this is making some more sense.

When you IPL the flash copy LPAR, everything is just a pointer to the existing production LPAR (until it changes). <--- correct

If you didn't change a single block of data on production, you'd in effect have nothing but
pointers to that data. Until you changed something on the flashed partition. <--- Correct, as long as nothing changes the live data

So you have:

Data that has not been changed on either partition <-- this data lives in the live partition
Original version of data that has since been changed on production <-- this is copied to the Flash partition
Data that has been changed on the copy partition <--- copied from live to flash before it is changed on the flash partition

And some serious magic that keeps it all in order. <--- it's all in that bitmap and a couple of simple rules!

So it would seem that you have to be careful not to touch your production data
in the flash copy partition until after you back it up. <--- but usually only the jobs backing up the data run in the flash partition!

If you for example cleared a master file [IN THE FLASH PARTITION] and then backed it up on the flash copy, my guess would be it would be as if you cleared it on production and backed it up. <--- correct

If you for example cleared a master file [IN THE LIVE PARTITION AFTER YOU MADE THE FLASH COPY]
and then backed it up on the flash copy, <-- you'd still have a complete copy of the data!

But even so, that's pretty fantastic stuff.




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