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[Discuss] raid issues


On Mon, June 23, 2014 10:37 am, Richard Pieri wrote:
> On 6/23/2014 9:41 AM, Stephen Adler wrote:
>> drives) and are the favorite for data centers. But there's a factor of 3
>> difference between the storage capacity and size. so the problem is that
> A 24x2.5" storage box takes up three rack units plus one for a server. A
> 16x3.5" storage box takes up 6-7 units plus one for a server so for the
> same space that the 3.5" box uses I can have 48x2.5" disks. 7 units for
> 48TB of raw capacity vs. 7 units for 96TB raw capacity. That's a factor
> of 2 at most and only with very expensive 6TB 3.5" disks. The factor
> drops to 1.3 with 4TB 3.5" disks and is even on with 3TB 3.5" disks.

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.

So for an extra 1U and 1.5x the cost I get 2x the storage and more speed
(because it's still the same number of drives, but 7200 v 5400 RPM).  The
running cost, of course, is a little more heat and power.

> There's the performance gain. Three 2.5" 7200 RPM disks together are
> substantially faster than a single 3.5" 15K RPM disk for less power and
> less heat which saves money on cooling costs and is good for drive
> longevity.

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?

> Dell still offers most of their *Vault line with 3.5" options. There are
> also plenty of bare chassis out there to build your own.


       Derek Atkins                 617-623-3745
       derek at   
       Computer and Internet Security Consultant

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