WD for examples sells 2.5" HDDs designed for A/V streaming. Dont Know how well it works if you do a lot of other stuff during streaming, too.
Best solution for timeshifting is ramdisk or ssd (be aware of the large amount of data writing and that ssds don't live forever) or a FAST hdd. 5400 or even laptop hdds are NOT perfectly suitable for this. But I don't want to make you nervous. In the most environments it works IF the server only streams.