SharePoint backup size estimation

Question

How to estimate the size of the database that need to be backup? I read some reference that the size is about 2.5*content database.
How about the backup size using back-spfarm? Is there any compression when backup as bak files? How to set the compression ratio?
So, is the full backup size calculated as 2.5*content database*compress ratio? And what is the differential backup size estimation?
Overall, I need to plan the space required for a weekly full and 5-6 differential backup.
Thanks for providing any ideas that I am not clear.

Answer 1

Hi, we are using a powershell script to calculate the SPSite size in MOSS 2007, same script could work in 2010 and 2013. The result from this + 6 % will return you the ruff size of the backup: It is working for us. Cheers
function Site-Space ($sitecola)
[reflection.assembly]::LoadWithPartialName("Microsoft.SharePoint") | out-null
$sitea = [Microsoft.SharePoint.SPSite]($sitecola)
[int]$sitespacesite = $sitea.Usage.Storage /1MB
$siterecyclebin = $sitea.RecycleBin | Where {$_.ItemState.ToString() -eq 'SecondStageRecycleBin'}
If ($siterecyclebin -ne $null)
ForEach($recycleitem in $siterecyclebin)
[int]$recyclesize = $recyclesize + ($recycleitem.Size /1MB)
$sitespace += ($sitespacesite + $recyclesize)
Else
$sitespace = $sitespacesite
return $sitespace