Here are some tips to make virtual workstation technologies perform better. Some of these are specific to VMware but could be applied to other virtualization platforms like Virtualbox.
For a new VM that you are creating select:
> Store Virtual disk as a single file.
If you have an existing VM make sure all of the snapshots are deleted (if you have taken any) and do this:
> vmware-vdiskmanager -r sourceDisk.vmdk -t 2 destinationDisk.vmdk
In this case the source disk will be the large VMDK file. After you convert you will need to edit the vmx (text based) file to reference the new vmdk file unless you used the same file name. Obviously you'd have to convert the disk to a new directory in this case or change the name. Once it's converted you will actually see 2 new files, one is the very small text file that defines the raw virtual disk file and the other is the raw virtual disk file itself. DO NOT LOOSE THE TEXT FILE! It is essentially impossible to remake as there is a special code in there that references the large raw file.
If you run the 'vmware-vdiskmanager' itself you can see all the options you can do.
Another tip is use multiple partitions to reduce the level of fragmentation. If you are using Linux format the partition with XFS or ext4. I normally give each partition 3-5 VMs and have partitions of 25-50GB.
Another tip is if you can use RAID 0 or RAID 1 of very fast hard drives. I am using 2 WD Raptor 150GB drives at home. I can run 4 VMs at once running a RAID 0 with 4 GB of physical ram. The key here is not necessairly MB/sec but I/O persec. This is where the 10KRpm drives rival any other SATA drive on the market by far. These disks are 50% faster. However if you use RAID 1 you will not loose too much if you use a quality drive like the WD RE3 1TB drive. This is one of the faster ones on the market. Do not worry about hardware vs. software RAID as the current processors have enough performance to lessen the need for hardware RAID (unless you have the money to burn).
I've also done a little research on whether or not to use Enterprise of 'RAID' type drives. There can be a sight advantage beyond the (in some cases) longer warranty and build quality. RAID supportable drives are designed to intentionally fail and even can send commands back to the RAID controller (software or hardware) telling the state of the drive. A standard disk will attempt retries for a number of minutes (typically 2) before it will announce a failure ultimately confusing the RAID software as it may have already declared the disk FAILED even if the disk recovered. Considering RAID type SATA drives will declare themselves failed in a short period of time (7-10 seconds) if it cannot recover and send the message to the RAID software. This behavior is specifically evident in the Western Digital line but are similar with other manufacturers and may not be a critical reason to choose these disks for home/test.