PA said:
Hi,
I am assembling a new PC and have a quick question... Should I put
more money buying a quad core processor and 1 HD 500GB or a dual core
processor and 2 HD 250GB in raid?
I was thinking in the first option, but a friend told me 2 HD working
itogether will make the pc faster.
I use relatively heavy databases and intensive statistical
programming.
Thanks in advance.
PA
Multiple core processors help, if there is thread-level parallelism
or program level parallelism. A quad core would help, as long as
the cores can be loaded well by the programs being used.
As an example, on some games, the loading pattern on quad cores
(and this is with thread-level parallelism), ends up at
100%-30%-30%-30%. Which means one core tends to be loaded more
heavily than the others. There aren't really many situations
where there is "perfect scaling" with the number of cores added.
Understanding how your applications are designed, and whether
they use multiple cores, is how you make the decision to go
with more cores or not.
I presume a database benefits from quick access time, and not
raw megabytes per second. Access time is dominated by seek
time on the hard drive controller. A number of drives have
been benchmarked here.
http://www.storagereview.com/Testbed4Compare.sr
A 15,000 RPM disk has lower seek time than a 10,000 RPM disk.
And SSD (solid state drives, either RAM based or flash memory
based) are faster and more expensive, than regular hard drives.
Being able to accept a smaller capacity storage device, would
make possible the usage of faster solutions.
(A single good 64GB SSD flash drive costs $2000. Good ones have wear
leveling, to prevent wearout of the flash chips due to limited write
life. Some of the tables here, show it is possible to get 10000 IOPS
from one of these drives. This company makes a driver that is
supposed to supplement the poor write performance of SSDs.)
http://mtron.easyco.com/news/papers/07-12-01_mtron-benchmarks.pdf
RAM memory is about $25 per gigabyte now, so to build a storage
device based on RAM, would cost about 64*25 = $1600 for 64GB of
memory parts, without considering the additional infrastructure
needed to make it work. The actual price charged by the companies
making them, is astronomical.
If portions of the database are frequently accessed, then caching
structures can help with that. If the database software has the
ability to cache frequently accessed info in system memory, then
the database performance may improve with time. It is possible
that adding additional memory to the computer, would aid in the
construction of a software based cache. It is better for the
database software to arrange such caching, as it understands the
structures better than any "dumb" RAID card you might add to the
computer.
Paul
