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## How to calculate disk space used to store backups on Data Domain

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## Re: How to calculate disk space used to store backups on Data Domain

VMware backups give you the ability to run a "full" by disabling change block tracking for a backup but there is not usually a good reason to do this unless the change rate of the VM is very high. Avamar still deduplicates the backup data either way, so the backups are "incremental forever" whether change block tracking is in use or not.

The general formula for calculating retention for contiguous days is:

s + (n-1)d

where s is the VM size, n is the number of days of retention, and d is the daily change rate (delta). It's n-1 instead of n because you have 29 days of change if you're keeping 30 days of backups.

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## Re: How to calculate disk space used to store backups on Data Domain

Hello, I'm trying to estimate the disk space needed to store backups on Data Domain. .I should consider the VM parameters: VM size, daily change .The backups settings:Daily execution, retention .Data Domain compresion ratio. My question is around the backup settings and how full backups are done. Could one of you clarify how Avamar backups are stored for a retention of 30 days ? .Option 1: Forever incremental => VM Size + (30 days x Daily change rate) = stored size .option 2: Full Weekly => (VM size + (7 x Daily change rate)) x 4 = stored size .option 3: Full Monthly => VM size + (30 days x Daily change rate) = stored size For year = (VM size + (30 days x Daily change rate) ) x 12 = stored size Regards Jean-Marc
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## Re: How to calculate disk space used to store backups on Data Domain

VMware backups give you the ability to run a "full" by disabling change block tracking for a backup but there is not usually a good reason to do this unless the change rate of the VM is very high. Avamar still deduplicates the backup data either way, so the backups are "incremental forever" whether change block tracking is in use or not.

The general formula for calculating retention for contiguous days is:

s + (n-1)d

where s is the VM size, n is the number of days of retention, and d is the daily change rate (delta). It's n-1 instead of n because you have 29 days of change if you're keeping 30 days of backups.

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