Why did WD switch to 2.5" for the velociraptors

[Compman55]

I thought overall 2.5" drives had quite a performance disadvantage over 3.5". If this is the case, is there a reason WD chose to go this route?

 

[OlafSicky]

Small servers

 

[corkyg]

The actual drive may be 2.5-in, but that is packed in a larger housing for cooling, etc. The overall size is still 3.5-in.

http://techreport.com/articles.x/14583

 

[Compman55]

I knew all along they are 2.5" in a 3.5" cooling fin enclosure. So that rules out the small server thoery. They used to be 3.5" completely, and then quite a few years ago they switched to 2.5" platter drives. I was wondering why.............

 

[biostud]

maybe 10K rpm + 3.5" is not possible, or shorter stroke distance for the heads.

 

[nehalem256]

While 2.5" drives lose out for raw transfer rate. I would they if anything have a latency advantage since their is less area for the head to cover. The primary advantage for 10K drives is lower latency, and perhaps WD figured that seq transfers were fast enough.

And it probably increased margins for them since they needed smaller platters.

 

[Lonyo]

Western Digital took a serious look at the enterprise market and determined they needed a product design that could compete in the widely expanding enterprise market where 2.5" form factor drives are taking a foothold due to the ability to pack more drives into the same chassis footprint. The other advantage to a 2.5" form factor is reduced power consumption, a hot topic in today's energy-aware world.

With that market in mind, Western Digital has moved to a 2.5" form factor with the VelociRaptor, while at the same time providing a unique 3.5" chassis mounting system for the enthusiast desktop market

The new VelociRaptor's 2.5" design utilizes two platters sporting 150GB each compared to the 74GB platter designs on the third generation product. These smaller higher areal density platters are beneficial in reducing the area the drive heads need to cover. This leads to an advantage in seek times and random access abilities of the drive when comparing it to its cousin, the Raptor WD1500ADFD.

We see a reduction in read seek times to 4.2ms and write seek times to 4.7ms. The one disadvantage is the drive's much smaller outer track diameter can potentially produce lower sequential transfers if not handled properly. Even with this potential pitfall, the drive's sustained transfer rates have increased from an estimated 84 MB/s to 120 MB/s.

Power dissipation improved across the board compared to the previous drive with a mere 6W or so needed to operate the drive during normal usage. Acoustic specifications remain the same, though this drive's noise characteristics are much improved, as we will see shortly.

http://www.anandtech.com/show/2508

 

[vss1980]

As Lonyo said.

There are other reasons not mentioned which, mechanically speaking, work in favor of the 2.5 inch format. It's easier to balance a smaller spinning mass, or I should say, it's likely to be less imbalanced compared to trying to spin a 3.5 inch disc at 10000 or higher RPM.
Apart from reduced power consumption, you're likely to get a bit less heat from the smaller drive also which is another bonus.

However, WD's move was not a big surprise. Even the last Quantum Atlas (before Maxtor and then Seagate) U320 SCSI drives, although 3.5 inch form factor only had 2.5 inch disc platters and I'm pretty sure that was before WD started doing anything like that with the raptors.

But to be honest, where I work we have over a hundred Dell Precision T7500 workstations all with WD 150/160GB 10K Raptor drives and whilst the speed impresses, and even the relative quietness of them, the longevity doesn't - they are by far the highest failing units.

 

[Emulex]

you do realize the platter size for the 15K sas and 10K sas and 10K sata are all 2.5"?

go look at a blown up pic of a 3.5" 15K SAS drive, its a super beefy 2.5" drive.

the velociraptor is just a regular WD25sas drive with a cheapie sata interface and a big heat sink for those who can't afford forced cooling. Honestly i'd take SAS all day long.

 

[Vinwiesel]

I have a 3.5" WD150 raptor which was easily the noisiest most irritating component in my computer. The only way I ever use it anymore is for temporary OS installs, or backups.

I assume they have gone smaller since it gives a better balance of IOP's and throughput while reducing noise/heat/power.