Leadership By Numbers

Category Administration
I have been asked to suggest the appropriate amount of free space on a Domino mail server, as recommended by IBM. I've always felt that 30 to 20% was about right (and on a SAN that number can be tightened up a bit). I'm confident that my range is correct, but with all the documentation I have, I can't find any definitive IBM recommendation. After all, Domino runs on so many operating systems, it's difficult to give a single answer.

So, I asked some key people and Daniel Nashed gave me his summary:

We have seen dramatic decrease of performance with low free space situations on all type of operating systems and have recommended in Lotusphere presentations that 20-30% free space is a best practice. Different file-systems behave in different ways when it comes to low free space situations but in all cases the result is very poor performance. Right now I am analyzing NTFS fragmentation in general with a customer not only specific to low free space conditions. The customer noticed that NTFS filesystems are really heavily fragmented after a while. Unix/Linux journaled filesystems work in a different way but also need free space.

I think recommending 20-30% is a good choice. But if you are talking about a address space of a terrabyte you might need a lower amount of free space (30% of a terrabyte might be too much). On the other hand for example a terrabyte of file-system size on Win32 is not desirable in general. I would split servers or at least split file-systems. That is what we do on Unix most of the times when we have server with this total disk usage.

It also depends how fast you can increase the size of your file-systems (if you are using a LVM and SAN storage it might be easier than with local disks ...) and also depends how fast the data is growing. Without archiving it normally grows exponential...

I'm sticking with my original estimate, and while Daniel is an authority on Domino systems management, I'll keep trying to narrow down something official from IBM.

On the other hand, it was interesting to see that Windows Exchange 2000 mail servers use a completely different method of measuring an appropriate degree of free space:

The multiple database and storage group feature of the Exchange 2000 Enterprise edition allows you to have multiple mailbox stores. However, be aware that you can only back up one database in a storage group at any one time (although you can back up multiple storage groups at the same time). At maximum capacity, you may have to back up 35 GB five times in your available backup window.

To perform an in-place restore, Microsoft recommends that your disks have at least as much free space as the size of the database itself plus at least 10 percent. For example, a 35-GB database runs on an 80-GB partition.