RPO Replication for TS7700 Disaster Recovery

Merle SadlerBy Merle Sadler

This blog is on the topic of the impact of zero Recovery Point Objective (RPO) for Mainframe Virtual Tape Replication focusing on the IBM TS7700 replication capability.

Have you ever thought about how much money you will need to save for retirement? I was talking with my financial advisor the other day and decided that whatever you think you need you should double. You can plan on having social security but if social security fails then retirement plans start to look not so rosy.

budget tradoffs for RTO and RPO

The same thing applies to computer systems. Customers spend a lot of time and money on Disk replication, reducing both RPO and RTO. But what if an application corrupts the data or a virus is uploaded? Corrupted or infected data is replicated just as easily as good data. This lends to making offline backup copies of disk files which also need to be replicated.

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How to Choose the Best IBM SVC/Storwize V7000 (Spectrum Virtualize) Replication Technology: Part I Introduction


By Brett Allison

Disaster Recovery Plan

Choosing the wrong V7000/SVC replication technology can put your entire availability strategy at risk.

For most customers, there seems to be a bit of a mystery in how replication works. On the surface, it is simple. Data is written to a primary copy and either synchronously or asynchronously copied to a secondary location with the expectation that a loss of data at the primary site would result in minimal data loss and a very minimal recovery effort.

There are several types of replication, and each type has its nuances. Each of these technologies should be evaluated in light of the following business requirements:

1. Recovery Point Objective (RPO): This is the amount of data loss expressed in time units (typically minutes) that you will lose should there be a failover to the secondary site.   Continue reading

The Attack of the Disk Clones


By Lee LaFrese


Attack of Disk ClonesWhen I first started working in the storage industry, the only way data was backed up was via tape. In the days of $10,000 per gigabyte of disk, there was no way any sane person would propose disk back-up.  The best practice for Disaster Recovery (DR) in these days was to create a nightly tape backup and then use PTAM (pick-up truck access method) to store it offsite. Applications were unavailable during the dump and the odds of successfully restarting after a disaster were typically not in your favor. DR testing was piecemeal at best and ignored at worst. In those days, the statistics suggest that many enterprises that experienced a major data loss due to a disaster simply went out of business.

Today, it is a different world. Cheaper disk, combined with the realization that most businesses need continuous availability, has led to replication schemes designed to avoid both data loss and downtime in the event of an unexpected outage. Point in time copy is used to make local disk clones to facilitate functions such as data mining, business intelligence, and rigorous DR testing. Straightforward backups are still done, but they now often use “tapeless tape” systems that rely on spinning disk instead of on magnetic tape. The net result is that instead of two copies of data (one on disk, one on tape), many enterprises now have more copies of their data than they can keep track of.  Indeed, this proliferation of copies has been a major influence on the explosion of storage capacity that has been going on. Although there are good reasons for all of these copies, it seems that our data centers are under siege by disk clones! Continue reading

Beneficial Use of GDPS Copy Once Facility (Experimental Evidence)


By Dave Heggen

There’s no law that requires GDPS implementations to use the Copy Once Facility for Global Mirror, but in my opinion, there ought to be.

The Copy Once Facility incorporates a simple idea: Copy Once describes a group of volumes without critical data; data that does not need to be continuously copied. An old version of the data on these volumes is sufficient for recovery. The beauty of the Copy Once Facility is that it is largely an act of omission: the volumes in the Copy Once group are suspended and withdrawn from the Global Mirror Session after the initial copies are completed. An additional feature of Copy Once is that you can periodically refresh the data in the DR Site if you want to. Refresh is only required if volumes move, if volumes are added or deleted, or if data gets resized. Some installations perform a refresh once a quarter as a matter of policy to ensure they have a valid copy of the data.

Some examples of good candidates for Copy Once are volumes that provide Data Set Allocation for data to be overwritten in recovery, volumes for which an old version of the data is just fine in case of recovery, such as my TSO data, and volumes for which only the VOLSER is needed at the recovery site, such as Work/Temp/Sortwk volumes. Continue reading