Backup vs Replication
Chris Evans is wrong:
"Traditional replication goes against the premise for which backups are taken - to recover to a point in time at which data was lost or corrupted....The second point (corruption) is probably the most important reason why traditional replication can’t replace backup - corrupted data would be replicated...In summary, traditional replication will not replace backup"
If "replication" equals "raid", then he is correct that logical corruption affects all copies, but then this solution is a bit unimaginative.
One tool which should be on everyone's list is rsync, which can do versioning on disk. In fact it even prevents the need for multiple copies of the same file via hardlinks, making it efficient enough for many scenarios.
Evan Unrue's claims are all valid:
"CDP replication mitigates the risk of replicating corruption because you have very granular restore capability being able to recover to a specific point in time"
I'm not sure that a point in time is necessary over an hourly or daily snapshot. Maybe for database records "point in time" is advantageous, but it's not obviously clear that it's always necessary to restore a file to the minute or second. For some, higher performance and efficiency may be more critical.
Claus Egge makes sense too:
Claus does a good job explaining how they can be unified.
His description of backup/replication contradicts Chris's.
Interestingly, Claus calls Continuous Data Protection a "backup" techology, while Evan called it a "replication" technology. Personally, I don't care either way since I acknowledge there is functional overlap.
"Yet, there is no technical reason for not eliminating tape entirely."
Ultimately, when it comes to capabilities, disks are supersets of tape. They can do anything a tape can do, and then some.
"you need both replication and backup because the two are not the same, and nor are they alternatives to each other...all need careful thought when building your backup strategy, and cannot simply be achieved just by implementing some form of replication."
While I have no specific disagreement, Phil seems to imply that they cannot be unified into a single solution that does both. CDP really blurs the lines as well. There's nothing wrong with being traditional, but Phil should consider updating his wording.