[Discuss] SSD drives vs. Mechanical drives

[bogstad at pobox.com (Bill Bogstad)]

On Sat, May 3, 2014 at 2:37 PM, Richard Pieri <richard.pieri at gmail.com> wrote:
> Bill Bogstad wrote:
>> And why does it matter that flash chips are slow?   The question is whether
>> SATA connected SSDs are slow.  The first 500Gbyte SSD that I looked at
>
> What do you think SATA connected SSDs are? They're banks of flash chips
> with a RAID controller and some DRAM cache. Just as RAID 0 with two
> spindles is ~twice as fast as a single spindle, RAID 0 with two flash
> chips is ~twice as fast as a single flash chip. Stack up enough flash
> chips and sure, you'll get performance that's better than a single
> rotating platter.

Again, so what?   I don't care if it is tiny monks with quill pens as long as
the price, performance, relability, and capacity numbers are good for the
system.  Now if you want to argue that single SSDs are less reliable
then single hard drives because internally they are RAID0 come out and say so.

>> (Samsung 840 EVO MZ-7TE500BW) claims a >500 Mbyte/sec sequential
>> read/write speed.   Lower capacity SSDs (fewer chips for internal RAID0)
>
> Samsung claims "UP TO" 500 Mbyte/sec sequential read/write speed. Actual
> values for that model fluctuate wildly:
>
> http://ssd.userbenchmark.com/SpeedTest/1519/Samsung-SSD-840-EVO-500GB

Thanks for pointing this out.   However, my first impression
is that it is still faster in both sequential and random read/writes
then a single
hard disk.  The worst sequential number is > 200Mbytes/sec from what I can tell
from that web page which beats most single disks that I have seen.

>> Newegg claims same Samsung SSD has the an active power consumption of
>> 0.24 Watts.   Here's some testing of a number of Samsung SSDs for
>> power consumption:
>
> It's not the watts. It's the watt-hours. A device that consumes 50% more
> power than another but operates 75% faster is the more efficient of the
> two. It consumes more watts -- joules per second -- but does so over a
> shorter span. More watts but fewer watt-hours. So, like I wrote, it
> depends on your usage but in general SSDs are about the same as HDDs in
> general use.

Only if you turn the storage device off when you are done with it.
With rotating rust
that has traditionally been considered the best way to kill a hard
drive.   Also, it isn't
clear to me what you are saying about the power usage for SSDs vs. hard disks.
My impression is that with SSDs and hard disk with capacities in the range of
500G-1000G, that SSDs are faster and use less power across a wide
range of use cases.   Sometimes by a factor of 2x, sometimes only 10-20%.
The only reason I can see not to go with an SSD for a drop-in
replacement is cost
or concerns about reliability.

Bill Bogstad