Independent disk vs dependent and Snapshots

[arcticeye]

Hi,

I read a lot of articles about independent disks vs dependent disks.

But I don't understand how the snapshots can be useful in an independent-persistent disk ??

Can anyone explain me?

And also, why independent-persistent disks wouldn't require backup of the VIRTUAL DISK and dependent would require backup.

Thank you!

Kind regards,

Matias

[narenotpp]

But I don't understand how the snapshots can be useful in an independent-persistent disk ??

Can anyone explain me?

- Independent mode virtual disks don't participate when you take snapshot of the VM.

And also, why independent-persistent disks wouldn't require backup of the VIRTUAL DISK and dependent would require backup.

Not too sure what you mean by above question. Refer the article where you read that statement please.

[arcticeye]

Hi,

Thank you for your answer and help!

The article which refers to independent disks not being necessary to be backed up is:

What are Dependent, Independent Disks & Persistent and Non-persisent Modes? | CormacHogan.com

Why Independent Disks?

This begs the question of what do Independent disks do for you, be they persistent or non-persistent. The bottom line is that if a disk is Independent, they can be omitted from a backup operation by virtue of the fact that they do not support snapshot operations. You can think of Independent as meaning ‘Independent of snapshots’.

I don't get it. I have many independent persistent disks and i DO back them up because if disk gets damaged I won't have any backup!

How do you see that?

Kind Regards,

Matias

[narenotpp]

It's because Backup solutions take snapshot of the powered on VM, then take backup of the VM as all the virtual disks are having their state preserved and new changes are being committed in delta files while backup job is going on, at the end of that backup job, snapshot will be deleted and VM continue to work.

In the blog you are referring , Cormac Hogan is not telling that backup is not important for the data residing on independent virtual disks, he is just mentioning that they are not included as it is when you run a backup job, because independent virtual disks don't participate in snapshots so in a way they are not being backed up as Let's say guest OS within the VM is still doing read/write with independent disks so backup software is not able to get the backup of it in consistent state.

now we have two possible solutions to take a backup of this, either I take VM offline and take a backup of that VM, or I install backup agent at guest os level and that way I take a backup of data residing in independent disk. as you have mentioned in the post, that you have many independent virtual disks which you take backup of regularly so I believe you are taking one of the two mentioned approaches.

Please refer following URLs for some more light on the subject

VMware KB:    Taking a snapshot fails with the error: Failed to take a memory snapshot, since the virtual machine is co…

Acronis Backup & Recovery 11.5 Help

https://www.vmware.com/support/vdr/doc/vdp_600_releasenotes.html

[arcticeye]

Dear Mr. Padmani

Thank you for your answer which I found very complete and clear.

When I first installed VMware I found many backup solutions but they were not free.

So I decided to make my own. I took a Script from internet and I adapted it to my needs. I use independent disks persistent so every week I turn the ERP and the Active Directory VM and turn it off (automatically) then a cron task executes the script and copies the vmdk and flat.vmdk files to another directory and then backuppc does a historical copy of the VM (quite redundant backup but I assure disponibility of the resources). I guest the most secure way to make backup is with the VM's turned off specially for ERP Software.

I know "my" backup system is quite manual and there maybe a lot of free and paid solutions much more advances.

Which one would you suggest? or do you think the way I'm doing this is not too bad?

Thank you again.

Kind Regards,

Matias

[brunofernandez1]

i think he is talking about RAW devices in phisical or virtual mode maybe?

[arcticeye]

Hello Bruno, no I don't. In fact I just want to know the difference and how could this be useful to use SNAPSHOTS in independent persistent disks. Just to understand what do they thought about when giving this option that i consider unuseful (snapshots+independent persisten disks)....:S

Thank you very much!