Question Probkup Vs Snapshot

Hello Everyone,
Is using Snapshot as replacement for PROBKUP ONLINE common? We were thinking of using Snapshot to take db back. To take a snapshot of our db it takes hardly 2 to 3 seconds (worst case 5 seconds). What are the pros and cons of using snapshot as replacement of probkup? Before starting a POC, I would like to get inputs from our experts.
 

TomBascom

Curmudgeon
If you do the snapshot wrong you will not have a usable backup. You generally won't find out until it is far, far too late. I've seen customers find out the hard way that their non-PROBKUP "solution" had been broken for months. That's a really bad place to be.

In spite of that -- carefully managed snapshots are very useful in some circumstances. After I have tested them and made sure they are actually working correctly, I like using them in migration projects or when testing new features and things like that. But I do not use them as a replacement for routine nightly backups.

Snapshots can also have unanticipated negative performance impacts. Sometimes you can find that in order to do perform an IO operation multiple layers of snapshot must be traversed. Like many things this is not a problem for typical generic workloads but it turns out to be a serious problem for a database. Like this for instance: https://kb.vmware.com/selfservice/m...nguage=en_US&cmd=displayKC&externalId=2000058
 

Rob Fitzpatrick

ProgressTalk.com Sponsor
Probkup reads the structure of the database from the control area (dbname.db), so it knows where every extent is located, even if they are distributed across directories or partitions (and even if the structure file is out of date). The potential danger with a snapshot is that someone grabs a copy of every database file *that they know about*, and they miss one, like the situations Tom alluded to above.

For example, maybe you have a convention that all database files reside in a certain directory or file system. But the regular DBA is away when an area fills up and someone adds an extent where there's room, in another partition.

Another potential danger is taking a snapshot when the database is not in a quiescent state. You could end up with copies of database files with inconsistent time stamps and again, an unusable backup.
 

cj_brandt

Active Member
it is common to replace probkup with snapshots and its a question commonly asked, well common for OE db topics...

when applying AI files to a snapshot, you will need to learn how to use the aisequence option of proutil.

probkup could still be used on the weekend until everyone feels confident with the snapshots.

worked with a company that has been taking snapshots for 10+ years and the only issue I can recall is one Rob mentioned. A new storage system was not taking the snapshot when it reported it was - it was delayed by several seconds so the db was not in a quiescent state when the actual snapshot occurred. It was discovered with testing.

One advantage of probkup would be having a utility scan the blocks of the db on a regular basis and if there was a physical corruption that occurred, it would be reported. A snapshot wouldn't help find that issue. I believe other utilities like a dbanalysis would though.
 
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