Do I Need this new Toshiba Harddisk?

These are so-called "A/V"drives, which forego error correction and recovery in favor of higher streaming performance where data integrity is not considered as important (for example, when you don't mind glitchy pixels in a multi-camera surveillance video recording system or TV show recordings on a cable TV HD PVR).

Al/V drives are also rated for 24/7 operation like "enterprise" grade drives used with servers, so heavier duty than consumer desktop drives.

Might work all right with Sonar if used exclusively for audio or sample files and for nothing else, but won't prevent faulty data from being written/read. Though not really needed for Sonar, I would think.

For higher disk performance, I'd consider SSDs, perhaps in a striped RAID 0 array (how we sometimes set up the old slow drives for more audio tracks in the early DAW days). Or maybe a WD Raptor or two.

What Jim said.

SSDs in RAID 0 would only make sense when max read performance is wanted which a single SSD could not provide, in a scenario such as when streaming samples or when mixing down a massive number of tracks.

SSD RAID 0 is perhaps not such a good choice for disk write (i.e., tracking, mixdown recording) scenarios where older data is being overwritten.

Probably better in any case to just opt for a faster (which might mean a larger capacity) SSD(s) as Jim suggests.