Greetings,
We have a 3tb Oracle 10gr2 database. We currently take a HOT backup as our backup method. The backup normally takes 7 to 9 days. If we use an RMAN online backup will that be faster to complete versus the HOT backup? Also will the compression be better being that this is a 3tb database?
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We have got 1TGB, full backup size with compression is about 250 GB, so it saves about 2/3 but this depends on the data itself.
Drawback - compression takes time, to compress and to uncompress as well.
To speedup the backup, rman can do backup in parallel threads (with hot backup this is possible as well of course)
DBAs prefer a cold backup because the backup is consistent across the board. More than anything, they like the comfort factor of a nice, consistent backup.
Hot backups will result in inconsistencies in the backed up datafiles.
RMAN will resolve these inconsistencies on recovery, after a restore. For many DBAs, it is a comfort factor.
If you perform a cold backup, you must have downtime for your database.
If you cannot afford the downtime, then a cold backup is not for you. If you want or need to perform a hot backup, then you must be running in archive log mode.
Cold backups are easy, do not require archived redo logs, but require downtime. Hot backups do not require any downtime, but are a little more complex and require archived redo logs.
Hi,
You ask if rman backup will be faster to complete. But do you really want that for hot backups ? Do you prefer a backup that thaks a lot of resources (i/o) during a short time or a backup that is longer but has very small impact on resources ?
RMAN will let you choose, and in both cases will use less resources (less redo generated, less block reads, even less with BCT, incremental backups, ...)
In addition, RMAN does a block verification (no need to do a DBV to check for block corruption)
But what is more important than the backup time is the restore/recovery duration.
RMAN will help you for that: incrementals, block recovery, ...
So for a 3TB database, I really recommand RMAN unless the hot backup is using something very fast at SAN level (such as 3rd mirror, BCV, ...)
Regards,
Franck.
It depends a lot on your setup but even without knowing it, I'll say RMAN.
Is your database Datewarehouse/DSS or OLTP?
To stress what mrjoltcola mentioned: Block Change tracking and Incremental.
What I haven't seen mentioned (if I missed it I'm sorry): incremental merge.
At a very high level:
You perform your initial level 0 (full). You only backup changed blocks with a level 1 (incremental). You merge that level 1 into the old level 0. You no longer have to apply 'N' level 1's to a level 0 to recover.
If you are not a high throughput OTLP system, this should be a lot faster.
Not sure if you chose FULL or LEVEL 0 INCREMENTAL. One caveat to note that is not intuitive:
A LEVEL 0 INCREMENTAL is another way of doing a full backup, but LEVEL 1 INCREMENTAL will only use the last LEVEL 0 INCREMENTAL for its comparison for incremental baseline purpose, not the last FULL backup. So if you plan to do incrementals, do not start out with FULL, start out with LEVEL 0.
I would have no way of knowing. It is all dependant on multiple variables (hardware, db activity, space utilization, RMAN channels).
But since even your RMAN backup is taking over 24hrs, the features we discussed above were developed specifically for databases like yours. You really need to implement incrementals (and BCT if you have Enterprise Edition).
I'm far from an RMAN expert but I think the level 0 is pretty much a datafile copy even if you specify compression. I believe compression is only for incrementals and archived redo logs.
A good guess on how long the initial level 0 will take: How long would it take to copy your datafiles from their current location over to where RMAN is storing them?
You should be able to watch the level 0 copy the files and get a good idea how far along it is.
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by: mrjoltcolaPosted on 2009-11-07 at 10:13:57ID: 25767336
RMAN will be faster and smaller
1) RMAN does not need to put the datafiles into hot backup mode to back them up
2) RMAN only backs up allocated blocks (whereas user-managed HOT backup backs up the whole file)
I don't use the compression feature, as it is an "extra option", so I cannot say.
You can take RMAN incrementals, and also use Block Change Trackign (BCT) with RMAN which will even more drastically speed up your backups.