Cheetah 15K.4: ST3146854SS – 146GB
It is in the Cheetah 15K.4 series that Seagate’s 15,000rpm drives first acquired the SAS interface. Before that, Seagate had provided HDDs with either SCSI or Fiber Channel. From today’s standpoint, all drives of that generation look roughly alike. Like its opponents, the 15K.4 series has a maximum capacity of 146KB achieved by means of four platters. The cache is 8MB large, like in the Maxtor. As for control electronics, we see a Marvell 88C7500 again and two chips from LSI (L2E2425 and L2A2661) on the bottom of the HDD.
Cheetah 15K.5: ST373455SS – 73GB, ST3146855SS – 146GB, ST3300655SS – 300GB
The next generation of the Cheetahs, 15K.5, has an increased maximum capacity (300GB, thanks to perpendicular recording) and a larger cache (16MB). The two LSI chips are replaced with one LSI L2A3075.
Cheetah 15K.6: ST3146356SS – 146GB, ST3300656SS – 300GB
As time went by, 300GB ceased to look like a big storage capacity and Seagate introduced another series called 15K.6. Thanks to the rapid development of perpendicular recording technology, the recording density had been quickly boosted by 50%, giving birth to SAS drives with 450GB capacity. These HDDs look different in comparison with their predecessors. The electronic chips are now on the interior side of the PCB. This ensures more protection for them, but on the other hand, the chips get hotter at work.
Cheetah 15K.7: ST3600057SS – 600GB
Finally, in the summer of 2009, Seagate rolled out the next update of its 15,000 HDD series. The top Cheetah 15K.7 model (with four platters and eight heads) offers an unprecedented capacity of 600GB. Besides, the interface has been updated: the new series supports both SAS 1.1 and the recently ratified SAS 2.0. We will soon devote a review to this new interface where we will discuss new SAS 2.0 controllers. We’ve got a simple reason for not paying much attention to SAS 2.0 now: as you will see shortly, the first version’s 300MBps bandwidth is more than enough for existing HDDs. Today, the transition to the newer version can only speed up operations with the HDD’s cache memory.
The 15K7 series comes with 16 megabytes of cache. Maximum reliability is a key factor for server storage and keeping a lot of data in the cache is not desirable.
Cheetah NS.2: ST3600002SS – 600GB
Winding up this introduction, there is a model with a spindle rotation speed of only 10,000 rather than 15,000rpm. But what a drive it is! The Seagate Cheetah NS.2 has a storage capacity of 600GB like the above-described 15K7. It is going to be interesting to compare old 15,000rpm drives with this model which has a much higher recording density but a lower spindle rotation speed.