Difference with backing up MS VM and Linux VMs

[mysen]

Hi all,

I'm new here but I thought I'd register seeing as I spend a lot of time on this website! and now I have a question.

Is there anything I need to consider on the physical layer when backing up both MS VMs and Linux VMs? I know at the application level that it's best practice to have all the same OS jobs grouped together which is fine, but I'm not quite there yet.

I'm designing how our backup server is going to communicate with the storage array, which at the moment I've decided to use the direct access approach with iSCSI. and the storage repository will be save back onto the SAN via an additional disk on the back (physical server).

Also, is there anything else I need to consider?
One other thing that I cannon find the answer to for the life of me... with the setup described above, will we be able to back up the servers during working hours without disruption? broad question I know.

Mysen

[veremin]

It's a broad question indeed that needs to be answered by real-life tests.

However, out of three existing transport modes Direct Storage Access is typically the fastest one, which means VMs' snapshots would be smaller and would take less time to consolidate, causing minimum disruptions.

Thanks.

[mysen]

Thanks for your reply. Do you know what state it would put both the types (OS's) of VMs in when backing up? I believe, maximum VM's there could be is 70 running at the same time.

Bottom line is, will they stop running if backups run during working hours? Will there be error should there be a query to a database at the time of the backup for example?

Regards,
mysen

[PTide]

Hi,

Do you know what state it would put both the types (OS's) of VMs in when backing up?

If you don't use any pre-freeze/post-thaw scripts or VSS (Windows) then OS will remain in it's normal state. If you use some pre-freeze script or app.aware processing then some applications might be affected (e.g. mysql can be prepared for VM snapshot beforehand to get transactional-consistent backup). The main difference is that if you don't put your applications in backup-ready state your backups will be crash-consistent so after restore from such backup your VM (and apps inside it) will behave like as if it was plugged-off.

will they stop running if backups run during working hours

They won't stop running, however freezes may occur during snapshot commit on a highly-transactional VMs. The better approach would be to backup logs (for MSSQL), not the whole VM.

Will there be error should there be a query to a database at the time of the backup for example?

Typically there should be no interruption in service, however thing might go wrong if you issue a large query with a significant amount of write requests targeting many tables in DB. As already mentioned - such apps as Exchange and MSSQL can produce very intensive change rate thus causing freezes and errors during snapshot commit, so it's recommended to take backups during backup window when the load on production storage is not so high.

[mysen]

Great reply, thanks very much.

I think our client will 99% of the time only need to run the backups out of working hours. However, there will be a need to backup during the day occasionally. I think in this case, we'll just have to accept the backup will be a version of the server that like you say will act as if it has been turned off.

Thanks for your help with this.

mysen

[veremin]

If you're going to stick to crash-consistent backups, kindly, test the backup or more specifically application recoverability - how well does application react to dirty shutdown. Thanks.

[mysen]

it will only be crash consistent for the very rare during the working day backups which I believe should be fine. I will document that the evening incremental backups should be application consistent.

Would you agree with this statement?

[veremin]

Correct, as long as you use application specific scripts as pre-freeze and post-thaw activities. Thanks.

[mysen]

I don't know what you mean by that. Could you explain more?

[veremin]

I mean if you want to have an application consistent backup of Linux VM running specific application, you will have to freeze activity inside this VM via pre-freeze script and unfreeze it afterwards, once the snapshot is created - post-thaw script.

Take a look at this section of our Help Center.

Thanks.