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Hard disk speed important to increase CFD computing speed?

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Old   October 16, 2009, 10:00
Default Hard disk speed important to increase CFD computing speed?
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lawrence law
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Hi,

Is the hard disk speed (rpm) important factor in CFD run time?

Wondering if i should upgrade to 10k rpm or higher or SSD.

Thanks
Lawrence
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Old   October 16, 2009, 14:35
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In general it does not matter much. If you are running a transient case and saving the time history to files every few iterations it may help some. It is much more of a factor if you do a lot of interactive post processing.
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Old   October 17, 2009, 01:46
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lawrence law
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Hi Kyle,

Thanks for the input. I was guessing that that would be the case. You have saved me a couple of hundred dollars!

Lawrence
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Old   October 18, 2009, 21:48
Default Go with a Raid 0 array
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I dont believe hard drive speed is a factor in cfd either.

However for future reference; if you want to increase hard drive speed set up a raid 0 array. This allows your computer to use multiple "cheap" hard drives at a time and gives you more speed than a single very expensive drive.
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Old   October 27, 2009, 12:30
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I have Raid 1 and when I read or write a file it's very useful I think.
When you autosave your files during a run it also helps to save time.
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Old   November 2, 2009, 06:46
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Robert C
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Quote:
Originally Posted by Maddin View Post
I have Raid 1 and when I read or write a file it's very useful I think.
When you autosave your files during a run it also helps to save time.
A RAID 1 configuration is a mirrored drive set up used for data integrity, not speed. In case of a single disk failure you an replace the drive without losing any data, because you have a mirror on the other drive.

You'd get a performance penalty using RAID 1 - but your data will be safer!
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Old   November 2, 2009, 07:01
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Hmm HDD benchmark says >250Mb/s, don't know what normal on single drives but this seems to be very fast.
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Old   November 3, 2009, 02:24
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Yes, 250MB/second is plenty fast... That is if you have enough physical memory. I did some meshing in gambit a while back and was able to exceed the physical memory by using the windows hard drive swap(definitely not recommended). It took a couple days instead of a couple of hours, but it worked so I cant complain. Certainly a hard drive speed dependent operation.

Personally, I would not build another system without RAID 0. Even disregarding CFD, you wont be disappointed. You never realize how much time you waste waiting on you hard drive until you get a RAID array.


Some good reference:

Single Hard Drive write performance(80mb/sec avg):
http://www.tomshardware.com/charts/2...hput,1013.html

Raid performance( 2drive 150MB/sec; 3drive 230MB/s): http://www.tomshardware.com/reviews/...S,1635-10.html

Cheers!
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Old   November 3, 2009, 04:15
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I have 8GB mem, more is too expensive. For same money I could buy a second computer with same hardware

I have looked, the 250MB/s are burst speed. Sequential read is ~120MB/s.
I wanted a mirrored raid because 1TB data's you can't backup every day...
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Old   November 3, 2009, 09:34
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Quote:
Originally Posted by Maddin View Post
I have 8GB mem, more is too expensive. For same money I could buy a second computer with same hardware
If that is the case, why not buy this second computer. Take out 4 GB memory and sell the computer with the other 4 GB...

And now a bit serious...
High speed disks are verry expensive, but it seems they will upgrade your performance (for finete element applications). It depends on the applications you run and on how your systems looks like and how you use it.
I have read some information about high performance computing and SSD disks. It seems for finite element analysis the use of SSD disks instead of 15K scsi reduces the I/O bottleneck. Besides that the biggest improvements were on power comsumption and space requirements.
When you run a big ass cluster, you will win alot when using SSD disk, but that is not what everyone is doing.

A cost effective solution migth be to instal 2 ssd disks of +/- 30 gb in RAID 0 config and use it for your working directories. Use a cheap ass slow hard disk for your data. Here in the Netherlands I can get 30 gb SSD's for 150 euro's. So this wont be verry expensive and I'm sure this will give a performace boost.

I am planning to get 2 SSD's within 5-6 weeks to set up a RAID 0 config on my XW8600.
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Old   November 3, 2009, 14:17
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No... I wanted 16GB memory but I haven't enough slots on the mainboard.
SSD I will wait a little bit. I make a lot of files for different tests and so are 30GB a little less
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Old   November 3, 2009, 14:46
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Sorry, I forgot something. When using two 30 GB disks in RAID 0 config, your system will see one 60 GB disk. But the speed doubles. With three disks it will see one 90 GB disk and the speed is trippled compared to the set up with one disk.

But if your files go up to 30 GB or more, the relative cheap SSD option isn't enough for you. Besides that writing one verry large file would not use the full potention of a SSD disk. When writing this kind of files SSD disks perform simular to 15K SCSI disks. Still pretty fast, but the SSD disk will really kick some ass when reading or writing a lot of small files.
... Perhaps not really the case in CFD world. I'm not really in to CFD, just starting to learn and perform some pump analysis. I know for FEA the SSD's really boost the overall computing performance.
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Old   November 4, 2009, 01:24
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I will look what I can get when I get new hardware
But I think a second computer with quad core would be bring more performance
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Old   November 17, 2009, 15:35
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I/O is still important, maybe not that much for CFD, but if your doing
cae in general its worth it. at the moment I am doing structural, CFD and acoustics..
My machine Dell R690 with 2 Xeon X5500 series, SAS drives and quadro GPU. I wouldnt wont anything else. 24 Gb of memory is also a benefit when running different models at the same time.

It depends on your needs: optimization and DOE is ALWAYS helped with the fastest workstation you can afford. Academic run once cases can be done with an outofthebox PC
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