Using object storage as a backup target
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SachmoNZ
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Reducing Storage in S3 after VM has shrunk.

Post by SachmoNZ »

Hi All,
Trying to get my head around this one.
*For this example let's assume there's no compression or anything when writing to S3. It's a simplified example and whilst not a major cost issue when the volumes are small it all adds up if your dealing with this with many VM's.

We are backing up a 10TB VM to a SOBR that consists of (VM is 1TB, 2TB, 7TB - 3 Disks)
A) Data Domain - Primary - 56 days retention (Backup daily, synthetic full on Friday)
B) S3 IA - Immutable - Capacity Tier - 56 Days - Copy immediately
Overall goal is all backups are copied to S3 immutable to protect against ransomware on prem etc.
Everything is working well - first backup went to S3 (took a while) and daily increments are going up fine.

So our backup chain would be anchored with a 10TB Full + increments that are copied up to S3. My understanding is the copy to S3 is forever incremental?

The question I have is..
If we were to remove 7TB of storage from the VM so it's now only 3TB - what happens in S3 to that backup chain? It's effectively based on an initial 10TB full and bigger than we need once the 56 days retention has passed?

To "shrink" what's stored in S3 is the best way to take an active full which will some how reduce the storage in S3 (either immediately or after say 56 days?)
or
Create a new job and start fresh?
or some other way?

As a side note is there anyway to see what the chain's look like in S3? For on prem we can use the files view but any way to view this for s3?
Thanks all

Sash :wink:

veremin
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Re: Reducing Storage in S3 after VM has shrunk.

Post by veremin » 1 person likes this post

If we were to remove 7TB of storage from the VM so it's now only 3TB.
How are you planning to do so? Remove virtual disk or simply deleting some files inside the guest? Thanks!

SachmoNZ
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Re: Reducing Storage in S3 after VM has shrunk.

Post by SachmoNZ »

In this case we dropped the 7TB vmdk but would be good to understand if it's any different in dropping a disk Vs removing data.

Gostev
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Re: Reducing Storage in S3 after VM has shrunk.

Post by Gostev »

In most file systems, deleting files does not change disk content (only MFT is updated).

If you remove a virtual disk, you should see S3 consumption reduce after 56 days have passed, since the objects representing removed disk blocks will not be a part of any restore point which is still under retention policy.

SachmoNZ
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Re: Reducing Storage in S3 after VM has shrunk.

Post by SachmoNZ »

Thanks Gostev - makes sense.

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