The trouble with holograms, if I understand them correctly, is that when storing information in a phase structure, to change one small part of the information you are storing, the hologram must be adjusted everywhere. The bits are encoded in a way that’s a bit nonlocal. I think a reasonable analogy is how small changes to a structure affect its Fourier transform. The whole thing leaps in Fourier space for a little wiggle in direct space. I foresee that being troublesome for write operations.
When cheap enough, write-once memories are much preferable over read-write memories, for archival and backup purposes.
Magnetic tapes are also normally used as append-only memories and very infrequently, if ever, they may be completely erased in order to reuse the cartridge and avoid buying a replacement.
While it is possible to use a magnetic tape like you would use a HDD, erasing and writing at random positions, there is no reason to do that, because it would be slow and it would not use fully the capacity of the tape.
It is likely that this holographic memory will be used exactly like a tape, i.e. append-only, but it will not be possible to erase the holographic cartridge.
If it would be possible to erase it, I would consider that as a deficiency, by providing an almost useless feature, which must be paid by a lower lifetime, as any material whose properties are reversible is much more likely to lose the information in time.
Write once is the only form of reliable backup. Once you start erasing data from an archive, you have introduced the most likely vector for losing data...human errors of judgement.
