There has been a bit of debate (okay, a LOT of debate) over what makes backup tapes truly “inaccessible”.  The California Assembly is on the verge of making that discussion moot.  From Law.com, this article agrees with their proposed new rule of evidence that it’s no longer necessary to consider backup data is presumptively inaccessible:

Zubulake’s bright-line test designating all disaster recovery systems as inaccessible simply does not apply in today’s world. It is likely only a matter of time before federal law reflects these advancements, rendering Zubulake inapplicable. Companies should therefore be wary of assuming that their disaster recovery systems do not have to be preserved and will not need to be produced.