How are mirrored disks used during a large read operation? Are they both used together or are they used one at a time?
How fast can a disk read or write data?
Benchmarking
How much slower is RAID-5 than a straight stripe when writing? Is there any difference when reading?
If you use the -o option you can graph the results of your tests at a later stage. Graphs based on output from dio provide an excellent I/O profile of a benchmark test which can then be easily compared.
Is my system paging a lot?
Paging/Swapping monitoring
Why is my system saying that it is constantly "waiting for I/O" when I know there should be very little I/O occuring?
Running dio against the swap devices (do swap -l to get device names) allows the user to watch paging/swapping as it takes place. Performance on such a system will almost definitely take a hit until something is done to relieve the memory shortage. dio can then be used to test the impact of measures taken to fix the problem.
How much data is written to /var during the course of a day?
Should I tune this file system to be fast for reading, writing or both?
Confirming I/O device usage
Why should I go to the bother of striping my file system? Does that much I/O actually take place?
Running dio against a supposedly busy partition could for example reveal how little it is used which would then impact future sizing/performance considerations. Conversely, it could show up "hot" disks that are being used constantly and may need to be improved some how.
How much throughput can I realistically achieve to a 4 DLT drive Jukebox using differential SCSI? Are all the drives being used?
Visualise I/O profile for overnight tape backups
What's the I/O profile for my overnight tape backups?
dio has been used very successfully to troubleshoot a Solstice backup system. By running dio against all the DLT devices in the jukebox overnight and graphing the results it showed that only 3 of the 4 devices where being used.
If you have any unusual or innovative ways in which you are using dio, please let me know and I will add it in here.