Databases snapshot in Vmware

most of databases such as SQL and Exchange mail servers , creates log files before they get committed to the Database.
If I understand VMware creates Delta file (Snapshot).
if I understand when the Delta file is created  new SQL logs will be created in the Delta file .
 Now when the Delta file(snapshot) gets deleted, will the logs be committed to the SQL/Exchange Database itself, or just  to folder in SQL/Exchange servers then the SQL/Exchange engine will be responsible for committing them to the Database ?

I have been told that Databases are not recommended to be snapshotted by VMware, but I cannot confirm that.

Any clarifications ?

Thanks
jskfanAsked:
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
most of databases such as SQL and Exchange mail servers , creates log files before they get committed to the Database.

Correct.

If I understand VMware creates Delta file (Snapshot).

If the hypervisor is tasked or manually created.

if I understand when the Delta file is created  new SQL logs will be created in the Delta file .

Not really, the OS and Application is unaware the snapshot has been create it lives outside of the VM. So logs will just carry on being created as normal.

Now when the Delta file(snapshot) gets deleted, will the logs be committed to the SQL/Exchange Database itself, or just  to folder in SQL/Exchange servers then the SQL/Exchange engine will be responsible for committing them to the Database ?

No, they will remain on the disk, and not flushed.

I have been told that Databases are not recommended to be snapshotted by VMware, but I cannot confirm that.

Any clarifications ?

Thanks

If that was true, VMware would not use them in their products to backup VMs e.g. in VDR, VDP, Consolidated Backup etc

Remember Most Backup Applications use the storage API, which include the snapshot process to backup a virtual machine. (you cannot get away without taking a backup without this method, VMware VDR, VDP and Consolidated Backup has used this by VMware)

This is how it's been since VMware launched their first Hypervisor - ESX 1.0.

We've been backing up VMs using the storage API (which includes) snapshotting the VM, for the last 13 years, and these have included Exchange, Active Directory, SQL, Oracle, and many other databases without issues!

Application Aware Backup applications such as Veeam, can sync with the application, and flush or committ the logs, before backup, and most applications are now VSS aware.
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jskfanAuthor Commented:
let 's say some Exchange or SQL logs are already queued up on the server and have not been committed yet, that's before the backup gets initiated.

When the backup starts,The backup App will quiesce the Client machine and send requests through VMware API to get a snapshot  created by VMware.
 the new logs from now on, will be written into the snapshot(Delta file). that SQL/Exchange does not understand
When the backup is finished, the backup App will send an API request to VMware to delete the Snapshot.
so when the Snapshot gets deleted at the end of the backup, are those uncommitted logs in the Delta file + uncommitted logs in SQL/Exchange server that were there before Backup started, will get committed by SQL/Exchange ?
can you put up a steps here how this can happen ?
Thank you Andrew.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
let 's say some Exchange or SQL logs are already queued up on the server and have not been committed yet, that's before the backup gets initiated.

When the backup starts,The backup App will quiesce the Client machine and send requests through VMware API to get a snapshot  created by VMware.
 the new logs from now on, will be written into the snapshot(Delta file). that SQL/Exchange does not understand
When the backup is finished, the backup App will send an API request to VMware to delete the Snapshot.
so when the Snapshot gets deleted at the end of the backup, are those uncommitted logs in the Delta file + uncommitted logs in SQL/Exchange server that were there before Backup started, will get committed by SQL/Exchange ?

Sorry the simple answer is no they don't get committed.

The only method that SQL or Exchange will be told to "flush" or "commit" the logs, if the Backup Application is Application Aware!

which has got nothing to do with the VMware Snapshot...

Why not try it out...on your SQL and Exchange Servers.....

Manually Take a Snapshot, Wait 60 seconds, Delete the snapshot....watch the logs, do they disappear - I can tell you no they dont!
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jskfanAuthor Commented:
I do not have the lab set up for it yet..
However, it makes senses, at the end of the backup , that the backup application will tell VMware(via API) to write the logs  that are in the delta file  to the folder where SQL/Exchange keep the logs. This way Sql/Exchange will commit the logs to the database
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I do not have the lab set up for it yet..

Okay.

However, it makes senses, at the end of the backup , that the backup application will tell VMware(via API) to write the logs  that are in the delta file  to the folder where SQL/Exchange keep the logs. This way Sql/Exchange will commit the logs to the database

If Enabled at Backup Time in the Job, and IF and ONLF IF the VMware Backup  Applicaton is Application Aware!

Not ALL Backup Applications are Application Aware.
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jskfanAuthor Commented:
Symantec NetBackup uses API to talk either to Vcenter and ESX host..
however I am not sure when it comes to Logs how are they processed...
Whether VMware just delete the snapshot(that contains most recent logs), and put them back with the logs that were in a folder of SQL/Exchange server , and will be committed by SQL/Exchange. It makes sense that way rather than VMware delete the most recent logs in the snapshot and commit them to sql/exchange database along with the logs that have not been committed  before the backup started...


Andrew:
 
Let's say the Backup solution we use is VMware Application aware..
how will it process the SQL/Exchange logs when the back up is finished ?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Symantec NetBackup uses API to talk either to Vcenter and ESX host..
however I am not sure when it comes to Logs how are they processed...
Whether VMware just delete the snapshot(that contains most recent logs), and put them back with the logs that were in a folder of SQL/Exchange server , and will be committed by SQL/Exchange. It makes sense that way rather than VMware delete the most recent logs in the snapshot and commit them to sql/exchange database along with the logs that have not been committed  before the backup started...

Yes, most backup applications, do as I have said. The logs do not move anyway, as far as the VM is concerned they are still in the same place on the disk.

Snapshots are Merged with the Parent Disk, and the VM should not notice this change!

So whether a snapshot is created or deleted, the OS does not know, what is happening outside of the VM.

Let's say the Backup solution we use is VMware Application aware..
how will it process the SQL/Exchange logs when the back up is finished ?

All logs are flushed into the main database.
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jskfanAuthor Commented:
Thank you
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