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.
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
Any unallocated or all-zero blocks will be de-duplicated. However, if a block is allocated and then freed, subsequent backups may still include the de-allocated block. If you know the empty space is unallocated, you can use the allocated space rather than the VM size for this calculation. However, the calculation will not be exact, so be sure to leave some margin of error. There may not be a perfect mapping between the size of the data and the used space on disk. There is always some overhead because files may not end exactly on disk block boundaries, etc.
ionthegeek
2K Posts
0
May 29th, 2019 06:00
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.
jmfleury
3 Posts
0
May 29th, 2019 05:00
jmfleury
3 Posts
0
May 30th, 2019 23:00
Thanks for the details. It helps a lot.
Regards
Jean-Marc
mkmouline
4 Posts
0
November 3rd, 2020 06:00
Hello ionthegeek
For Example : VM=Size = 200 GB
Daily Change Rate is : 5%
30 Day Retention :
The Backup need is : 200 + (30-1)*5% = 200 + 29*0,05 =201,4 GB
Is it Right ?
Thank You,
ionthegeek
2K Posts
0
November 3rd, 2020 08:00
The delta value should be in some unit of bytes. If the change rate is 5% of 200GB, the delta value would be 10GB giving you:
200GB + (30 - 1)*10GB
= 200GB + 29 * 10GB
= 200GB + 290GB
= 490GB
mkmouline
4 Posts
0
November 3rd, 2020 09:00
Hello,
In practice the used space of the VM is < than the VM Size.
On our example for VM size = 200GB the used space for example is 50 GB.
Is this parameter (used space) can be used on the formula ?
Thank You,
ionthegeek
2K Posts
0
November 3rd, 2020 10:00
Any unallocated or all-zero blocks will be de-duplicated. However, if a block is allocated and then freed, subsequent backups may still include the de-allocated block. If you know the empty space is unallocated, you can use the allocated space rather than the VM size for this calculation. However, the calculation will not be exact, so be sure to leave some margin of error. There may not be a perfect mapping between the size of the data and the used space on disk. There is always some overhead because files may not end exactly on disk block boundaries, etc.
mkmouline
4 Posts
0
November 5th, 2020 00:00
Hello Ian,
What about adding paremeters like :
Groupe1 of VM : have for exemple 1 Full Backup every Week and 3 month retention
Group2 of VM: having 1 Full Backup every Day with 3 month retention
How can we estimate the backup storage need
Any tips will be very appreciated,
KamalMouline
2 Posts
0
November 10th, 2020 09:00
Hello Ian,
The same formula can be used when we have Avamar/Datadomaine integrated with vCloud Director ?
Many Thanks,