How large a TFile or TTree can be?

ROOT
,
1

Hi all,

The central question is in the title.
How large can ROOT file actually be? What is the limit?
Could it be 100 Gb? 1 Tb? 10 Tb?
Is it limited by other factors? E.g. TTree or Branch size should not exceed X?

I didn’t really find any info on this, except very old posts about ROOT 3 and 4.

EDIT:
I am also interested, because I want to know the limit on how many files I can hadd.
As it seems, there might be some problems with very large combines e.g. (post)

2

The only current limitation is the number of baskets in a TTree (50 millions baskets accumulated across all branches). The resulting size depends strongly on the number of branches and the size set of the Cluster/TTreeCache. If each basket is 32k (default but not typical size) that lead to 1.5 TB single and it can be much bigger if the baskets are bigger.