Huge backup_client.db on mail server


My mail server VM ran out of disk space today. Short investigation lead me to discover the backup_client.db file was 7.5GB. On my other servers, it’s under 100MB.
The mail is stored in maildir format (so millions of small files)… Is this going to create a huge database? Should it be that big?

Is there a command to “compress” or otherwise reduce that size?


It stores the client-side hashes there. Are those enabled?


If that’s the default, then I assume so. Where would I check?
The local full and incremental file backup transfer modes are both set to hashed. Is that it?


So we’re not quite 2 months later, and this file has now grown to 14GB! There’s only 9GB of data on the entire rest of the the server.

Where should I be looking to disable the client side hashes? What impact will that have on the backup process?


Using separate setting, for that client only you can try 2 things
On internet, tab you can uncheck client hash.
In the advanced tab switch from hashed to raw transfert.


Just coming back to this again… It’s grown to 15GB since I deleted it in January. I had it set to raw for every setting in the advanced tab, but noticed I missed the client side hashes in the internet tab. Changed it now, but I have doubts it’ll do anything.

Still confused how the hashes for ~10GB of files can take 15GB to store. It’s emails, so lots of small files, but surely the hashes are still smaller than even the headers of the emails.