From an academic standpoint, when does it make sense to use Advanced Disk over MSDP?
The scenarios I've seen from reading are:
1. Data that is about to get dumped to tape
2. Data that is being kept for a very short life span
3. Data that changes wildly from day to day and does not dedup well
For #3, how much change does there need to be to make it worth it?
The non academic part of this question is I'm using two appliances, one intended for a DR role and am looking at utilizing AIR replication between the two sites. However it appears that Advanced disk is not supported by AIR. I'm entertaining the idea of converting ALL of my storage over to MSDP, so can anyone tell me why that's a bad idea?
I would only say #3 is relevant, the other two would have been valid in the days when rehydration was slow.
How much change does there need to be to make it worth it? That really is up to you, the dataset and the space available in the pool. If you've got a 1 TB data set that gets 50% dedupe and a 4 TB pool you can get 8 copies in a dedupe pool, and only 4 in ADV pool. So you might say that's worth putting it in dedupe. If the dataset only get 25% then it all changes and you might just accept a reduce retention and keep it in ADV so there is more space in your dedupe pool for other backups to use that get 95% dedupe.
Remember that the dedupe ratio influences the decision, but not just the dedupe ratio of the "bad performer" but also the dedupe ratio of the rest. Space used by a 2x (50%) performer could be utilized by a 20x (95%) dataset. Like for like that is a huge difference and impact.
These are both variations on #2...
#4 Data that needs to be backed up NOW, not when the next job slot opens on the Dedup pools.
We have Informix and DB2 logical logs that auto-dump to NetBackup and I route them first to an Advanced Disk pool then to Dedup via SLP. Sometimes the DB2 system is kicking out more than one log a minute so time is of the essence.
#5 Data that is going to be restored but doesn't Dedup/rehydrate well.
Informix is the worst when it comes to Dedup percentage and rehydration is also slow. For our weekly restore of Prod->Dev the database backup gets copied over to Advanced Disk (and that copy gets promoted to Primary) before the restore starts.