For VOD, the first bottleneck is almost always the number of reads your hard drive can support. If you are using an SSD you will be able to do much more than you could with an HDD. However, even with an SSD, it will be your initial hurdle. The important factor to look at for drive speed with an SSD is the Sustained Write Speed (NOT peak burst write!). That Sustained Write Speed will determine the absolute ceiling of streaming bitrate you can achieve from your disk.