[Discuss] raid issues

[Richard Pieri]

On 6/23/2014 10:53 AM, Derek Atkins wrote:
> I've already showed a counter-example showing this incorrect..  You can
> get a 24x3.5" 4U case.  So for an extra 1U I can get the same number of
> drives, which gives me 2x-3x on space (largest 2.5" drive I can see right
> now is 2GB, vs 4-6GB 3.5" drives).  Of course the 2GB 2.5" drive is only
> 5400RPM, and as of right now costs $118 from NewEgg, versus a 7200RPM 4GB
> drive for $184.

I'm going by what I have in my server room right now. You can get a
denser 3.5" chassis but you can also get a double-ended 2.5" chassis
which doubles the number of disks: 48x2.5" in just 3U of space. 24x3.5"
at 6TB is 144TB raw. 48x2.5" at 2TB is 96TB raw. That's a factor of 1.5.

Any place you can fit a 3.5" disk you can fit at least three 2.5" disks.


> That presumes you do run more 2.5" drives than 3.5" drives.  And doing so
> drives up the cost.  To get the same amount of space I need 2-3x the
> number of 2.5" drives.  At that point is it really still a power/heat
> savings?  Are 2.5" drives really using less than 33-50% of the power of a
> 3.5" drive?

About 60% less. Seagate 15K RPM Cheetah SAS disks have an average power
draw of 16.31W. Seagate 7200 RPM Constellation SAS disks have an average
power draw of 6.35W. Data taken from Seagate's current spec sheets.

-- 
Rich P.