Our latest event “IT-Pro Chalk Talk” co-hosted with Winsec & IT-Talks was very interactive and several questions arose during that session. 
http://www.pro-exchange.be/blogs/events/archive/2010/02/04/event-it-pro-chalk-talk-session.aspx
This is the first question that I will summarize what we all talked about.

Question : Exchange Backpressure keeps kicking in because of diskspace issues and we don’t really know where to look for

Background : If Exchange Backpressure kicks in then All message flow stops, and the server rejects all new connections and messages. (Hub Transport server)
More information here : http://technet.microsoft.com/en-us/library/bb201658(EXCHG.80).aspx

Answer :

Monitor the disk usage on the Exchange Server if possible :

• Use Performance monitor
• System Center Operations Manager
• Other tools …
• Use alerting to inform disk space usage

If diskspace is already low and you want to find out what folders are very big:

• You can use Diruse.exe
• Windows 2000 Resource Kit tools : http://www.microsoft.com/downloads/details.aspx?FamilyID=955D7F2F-73D9-4018-9DD7-42DA210E62EE
• Windows XP SP2 Support Tools : http://www.microsoft.com/downloads/details.aspx?FamilyId=49AE8576-9BB9-4126-9761-BA8011FABF38
• Commandline tool that displays disk usage per folder so you can easily find which folders are very big

Pagefile:

• Move Pagefile to another disk/volume
• manually configure page file options
• Check “Ask the performance” Team blog on Memory Management http://blogs.technet.com/askperf/archive/tags/Memory+Management/default.aspx
• Virtual Server or Physical Server should have the same Virtual Memory configuration

Additional:

• Disable backpressure as a last resort
• Use mount points to use other storage/disks