8 IBM ProtecTIER Implementation and Best Practices Guide
Visibility switching The automated process that transfers the visibility of a
VTL cartridge from its master to its replica and vice
versa. The visibility switching process is triggered by
moving a cartridge to the source library Import/Export
(I/E) slot. The cartridge then disappears from the I/E
slot and appears at the destination library's I/E slot. To
move the cartridge back to the source library, the
cartridge must be ejected to the shelf from the
destination library. The cartridge then disappears from
the destination library and reappears at the source
I/E slot.
Principality/ownership An attribute set at the repository where an individual
cartridge can be updated or written to by a backup
application. A cartridge at its principal repository can
be in read/write (RW) or read-only (RO) mode. At other
sites, it is always RO. Each cartridge has enabled
principality/ownership for one site only.
Dirty bit The dirty bit attribute (in-sync) helps identify
consistency points during disaster recovery (DR).
When the dirty bit is off for a cartridge at the hub, this
cartridge is fully synchronized with the spoke. During
DR, that cartridge is fully synchronized, not only at the
consistency point, but also after the last replication
occurred. If a cartridge is out of sync during DR,
determine the particular consistency point to which the
cartridge adheres. Generally, the cartridge adheres to
the consistency point that was established the last time
the cartridge was fully synchronized.
Disaster recovery Disaster recovery (DR) is the process of recovering
production site data at a remote location. It includes a
way to indicate to a remote repository that the
production site went down and notifies administrator to
initiate data recovery process.
Failover Failover is a process of enabling the production at
remote site in case of the critical event or disaster at
the primary site. It can be initiated intentionally if the
primary site is under threat of a catastrophe and it is
beneficial to perform takeover at the remote site with
full control.
Failback A process that is initiated from the remote site when
the source site is again available for operation. The
process ensures that the paired repositories are
resynchronized using the least amount of bandwidth
and maintaining the most recent copies of backups.
1.2 ProtecTIER basic concepts
ProtecTIER is a virtual tape product that appears to the backup servers as a standard tape
library with a robot, cartridges, and tape drives with support for
LAN-free data streams from
the hosts. As data is written to this virtual library, it is examined for identical blocks of
information that is already added to the repository.
Chapter 1. ProtecTIER basics 9
This identical data is not stored again in the repository; it is referenced as duplicate data and
reduces the amount of disk space required. This process is known as deduplication. The
engine for deduplication is called
HyperFactor.
For the deduplication process to work effectively, the data that is sent to the VTL must not be
manipulated, that is, modified as it passes from the disk drive on the client server to the VTL.
Any change reduces or eliminates the ability of the HyperFactor engine to recognize a
subsequent version of it.
Figure 1-1 shows the relationship between HyperFactor (HF) processing and the respective
storage savings.
Figure 1-1 Storage savings with ProtecTIER HyperFactor
The effect and result of HyperFactor processing is a factoring ratio. In simple words, the
factoring ratio is the ratio of nominal data (as a sum of all user data backup streams) to the
occupied physical storage in ProtecTIER repository.
There are two key elements that impact your factoring ratio and effectiveness of your
ProtecTIER environments:
Data retention period The period, measured in days, for which the backup application
keeps the data available in its disk or tape repository. Typical
retention periods of user data and applications are not longer than 90
days. Typical retention periods for database backups are not longer
than 30 days, but specific weekly or monthly snapshots can be
stored for months or even years.
Tip: A longer retention period increases the factoring ratio of your ProtecTIER product.
Deduplication Efficiency with ProtecTier
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10111213141516171819202122232425
HyperFactor Ratio
Storage Savings [%]
HF Savings
15 93.3
10 90.0
580.0
475.0
366.7
250.0

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