Hey Cheddar, more computer questions...

Joelsbass

Had a few things I was wondering about...

So i'm going to see a speed diference between running say 4 250gb drives vs 2 500gb drives right? how far down do you go in drive speed before it stops having a large effect? and does tying in a large external HDD for storing less speed sensitive items slow other things down? I was thinking about picking up a large external soon to back up my music and umm.... other.... stuff.... if that would work well then I could go even smaller on the system drives and keep my movie/tv show playback speed up...

Would smaller high RPM SCSI drives show a large difference over the 7.2krpm SATA drives? Also when it comes to buffer memory I'm sure more is better but how much of a difference is there between 8 and 16, and again between 16 and 32? Mainly asking because of the External HDD's I'm looking at, the 32mb is about $50 more in the 1TB range than the 16mb...

Any insight you can provide is greatly appreciated

cheddar

Actually the speed matters most for things like games that have to read large amounts of data off the hard drives during gameplay. Or for other data intensive reads like boot ups and the like. As long as your computer isn't parallel processing something else when you're watching movies, you should be ok without going for speed demon scsi or sata high rpm drives. IDE drives like a DVD are much slower than the HDD, but they still play movies just fine.

A large external drive will not affect your other drives unless it's in use while you're watching a movie. Say you're trying to copy something over at the same time.

RAID will probably be overkill for your movie watching needs. I mainly mentioned it 'cause people aren't really backing up their home HDDs these days. Considering the amount of digital stuff we store on them now -- movie collections, digital family pictures, financial records etc. RAID provides some nice redundancy capabilities just in case the HDD goes down. Old school, you always had the negatives in case the dog ate your family album. These days, the pictures are erased from the camera and put on the family HDD. And one pffft later, all your stuff is gone.

Since you aren't really building this as a gaming machine, I would shop for drives looking for low noise, reliability, and capacity over brute speed. Read some reviews on the the web and see what people are recommending. And once you have the raid hardware, adding internal drives is much cheaper than buying external ones.

Joelsbass

Maybe you can help me figure out why my I-tunes TV shows keep on lagging (for lack of a better word...) the audio keeps going but the picture keeps skipping... it's REALLY annoying... I'm gonna see if it does it with a DVD (haven't used it for that in a while) maybe my drivers are off or something...

cheddar

Now we may be talking about a lot more than hard drives. The CPU (central processing unit) and GPU (graphics processing unit) have a lot of calculations they have to make to display an image and synch that with an audio track. If there's a bottleneck somewhere, the whole thing gets out of whack.

I sometimes watch broadcast HDTV and SDTV off my computer. Depending on what else my computer is trying to do at any given moment, the audio and video streams can go out of synch as the additional stuff takes cycles away from the processors. And I have a dual opteron system. Once the extra cycles are freed up, the video settles down again. A faster system overall may solve your problem.

I thought of some additional things about RAID from your question. Two 500 GB HDDs are limited to RAID 1 mirroring for back-up. That means you have at most 500 GB of space to use. However four 250 GB HDDs can use RAID 5 for back-up. Which means only one drive has to be used for redundancy. So you get 750 GB of actual storage space. You can see the advantage this gives you over an external drive. If you buy a 1 terabyte external drive, you're talking about $400-$500 dollars and are limited by the usb or firewire or worse network interface. However, if your RAID hardware supports say 6 HDDS, you can buy 6 250 GB drives for $60 or $70 a pop. So for $400, you can have 1.25 terabytes of usable space (still one 250 GB drive for redundancy) all at a much higher internal transfer rate and insulated against a single drive failure.

Of course you will have to get quiet drives. And make sure your case has good ventilation and nice quiet 120mm cooling fans. Seagate usually gets good marks for noise. Western Digital is the other major manufacturer. I actually have four of WD's raptor drives in my system. Again, probably overkill if you don't game much. Maxtor makes really cheap drives, but I've read that they have problems with some raid cards like rocketraid. They could have problems with other RAID hardware as well. Rocketraid makes some nice cards that support like 8 drives. But there are a lot of inexpensive motherboards out there with built-in 4-6 drive SATA RAID.

BaggedLancer

Cheddar,

I thought my understanding of raid(very inexperienced) was that for an example you said of using 4 250's only 2 of those would be usable space. I.e. for every gigabyte you want to backup you need to have equal on the other end.

So 4 250s would leave with 500g of usable space, since 2 of those 250s are mirroring the 2 being used.

Raid 5 is a striped raid, meaning the data is split between all the drives. I believe what you are referring to is either a raid 0+1 or raid 1+0 if you want it to be mirroring.

According to these links Raid 5 is nothing but striping data, which leaves no backup.
http://en.wikipedia.org/wiki/Nested_RAID_levels
http://en.wikipedia.org/wiki/RAID

cheddar

BaggedLancer wrote:

Cheddar,

I thought my understanding of raid(very inexperienced) was that for an example you said of using 4 250's only 2 of those would be usable space. I.e. for every gigabyte you want to backup you need to have equal on the other end.

So 4 250s would leave with 500g of usable space, since 2 of those 250s are mirroring the 2 being used.

Raid 5 is a striped raid, meaning the data is split between all the drives. I believe what you are referring to is either a raid 0+1 or raid 1+0 if you want it to be mirroring.

According to these links Raid 5 is nothing but striping data, which leaves no backup.
http://en.wikipedia.org/wiki/Nested_RAID_levels
http://en.wikipedia.org/wiki/RAID

RAID 5 is indeed striped so there is an advantage in speed over a single drive. However, it is parity level back-up. Since all digital information is either 1s or 0s, you can add up the bits across an array and store the result of that addition as either an odd or even bit as back-up parity data. This only requires one drive as long as they are all of equal size. Then if one drive in the array goes down, you can rebuild the array by figuring out if the missing bit is a 1 or 0 from adding up the bits on the remaining drives and the parity information tells you what the missing bit is 'cause you know the addition has to either be odd or even.

That's why RAID 5 is a popular back-up option 'cause it scales beautifully as only one drive is needed for the back-up information. It only works if one drive fails. Having two drives fail at the exact same time is unlikely, though. And they could just as well fail on both sides of a mirrored array for that matter.