MTU Email Conversion - Efficiencies

Storage and Backups

We now use a lot less disk space for checkpoints and a lot less tape for incremental tape backups with the maildir format. Since the mbox format concatenates all of the mail in the inbox, or folder, into one file, that file is changed every time you add, delete or move a message. Almost every user receives mail every day so that file is changing frequently. When it comes time to checkpoint the file we basically have to make a complete copy. For example, my inbox is currently 44MB. Since I receive mail continually throughout the business day I will have to basically create 220MB in checkpoint files in a 24 hour period. The same thing happens with the nightly tape backups. If the inbox is changed even once during the day we have to backup the entire file. We currently do a full backup of mail on the weekends and incremental during the week. The percentage of change is so high that we end up backing up 80% of all of the mail during the incremental.

Since the maildir format stores each email as an individual file the percent of files changed during a business day is more like 5%. For example, my inbox has 667 messages in it. I receive 30 new email a day and delete 15 of them. Now my percent of change for purposes of checkpoints and backups is 2.24%.

Before conversion, University mail home directories are allocated 1,008GB of disk space and the checkpoints are allocated 645GB or 63.94% of the home directories. By changing to maildir this percentage will change to 10% - this allows an increase in mail quotas.