It all depends on how your storage is structured within your organisation. Tier 1 would typically be your most resilient (and more expensive) storage system - e.g. DMX, whereas your Tier 2 may be served by a cheaper storage system - e.g. Clariion.
You would certainly put your database dumps on Tier 2 storage if you can - you don't want something like a backup or dump to be taking up valuable disk space on the more expensive disk which could be used for your more mission critical systems. What goes onto Tier 1 and Tier 2 would be a policy decision within your organisation.
Also you could have both Tier 1 and Tier 2 on the same storage system. Tier 1 might be faster fibre disks, whereas Tier 2 may be something like higher capacity SATA disk, assuming your storage array can handle this.
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