Quantum DXi4701, Руководство пользователя

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Chapter 1: DXi4701 System Description
Hard Drive Storage
16 Quantum DXi4701 User’s Guide
Figure 5 VTL Example
Virtual Media—How Many and What Size?
There is no correct answer to this question as it really depends on your
backup regime and the backup application in use. A DXi system does
not preallocate disk space when a virtual tape cartridge is created, there
can be an inclination to create a lot of large virtual tape cartridges,
greater than the amount that is actually required. While this has no
initial bearing on the DXi’s capacity utilization, it can cause issues down
the track.
Regarding the quantity of virtual media you need to create, as long as
there is sufficient media to hold the amount of backup data for the
required retention period, the quantity does not really matter. However,
it is extremely important, as mentioned earlier, that the aging and expiry
rules of the media pool are defined early. If these rules are not defined,
the virtual tape cartridges will never enter the scratch pool resulting in
you running out of virtual media, and in turn space on the DXi system.
As a rule of thumb, more is better than less; as long as expiry rules are
defined.
Although there is no perfect size when it comes to creating virtual tape
cartridges, there are a few factors to consider. If a virtual tape cartridge