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SCSI vrs IDE RAID 0 Need Purchasing Help Badly!!

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  • Hard Drives
  • NAS / RAID
  • SCSI
  • Storage
Last response: in Storage
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October 24, 2001 4:40:49 AM

I am currently deciding what HDD's to put in my new system. I first wanted to buy 2 (Cheetah X15 36LP 18.4 GB Ultra160 SCSI 15K RPM Drives) and attach them to an Adaptec SCSI RAID 3200S controller. The other alternative would be Two - IBM Deskstar 60GXP 40GB 7200RPM ATA100 connected to a Promise ATA/100 Raid 0 Controller Card. Basically I dont care about the cost or "wasting money" I'm just looking for the best performance. The company that I contacted gave me this information :::

The IDE drives would have a max data transfer around 40M/s while the SCSI drives would top out at 29M/s. So even with the incredible increase in access times with the 15k drives they would overall perform slower.

Could someone who understands this stuff a lot better than me please!!! respond to let me know if this makes any sense. This will be the last computer that I buy for at least 3 years and really dont want to cut any corners that I will regret.

Thanks In Advance for the help!!

More about : scsi vrs ide raid purchasing badly

October 24, 2001 5:45:10 AM

I have yet to see an IDE drive sustain that pace in real world usage. Given that your disks will fragment over time, the access time will certain figure in later on. Of course, RAID will improve things a bit. Somehow, I don't think the IDEs will be faster (throughput-wise) than the SCSI's. Perhaps the company got their numbers the wrong way around. Finally, SCSI has other benefits, including lower CPU utilisation and much better bus contention/sharing. I think that the SCSI bus multitasks much better than an IDE one.
October 24, 2001 5:54:18 AM

i have an ide raid w/2 60gxp's on a promise tx2 controller, i get 42mb/s-43mb/s sustained. yes scsi does have other benefits. but it's not like accessing an ide raid will shoot your cpu usage up to 60% or something. it's small, especially with todays cpu's, they can more than handle it.
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October 24, 2001 6:27:37 AM

Sorry for being anal, but you claim your throughput is 42-43 milli-bits per second!

I have a Maxtor Diamond Max (ATA-66) drive on an ATA-33 bus... I've seen it burst to 29MB/s when my CD Burning software is testing throughput. But, when I copy GB around (e.g. huge database files), my throughput rarely comes close to half that. So, I find it interesting that RAID on an ATA-100 controller makes such a difference! Perhaps I should check my bank balance ;) 

I would be willing to bet that a SCSI based system would feel more responsive, especially when dealing with lots of really small files. Based on prior experience with a SCSI-based PPro200, it would also grind less when thrashing the virtual memory... but then perhaps with today's memory prices that isn't an issue ;) 
October 24, 2001 4:07:37 PM

Are you getting 42 to 43MB/s by testing the single drive or by testing them in the RAID 0 configuration? (I.E. 21MB/s per drive?) Sorry if these are lame questions I'm slow :) 
October 24, 2001 6:30:51 PM

Malc, is that a 5400RPM or 7200RPM drive? That makes a much bigger difference than the interface.

BTW, the two SCSI drives will eat the two IDE drives for lunch. The company that told you 15 vs 20 is full of crap.

<font color=green>I post so you don't have to!
9/11 - RIP</font color=green>
October 24, 2001 6:40:25 PM

I have two IDE drives, one 7.2K and the other 5.4K. I was referring to the 7.2K. And yes, I think I do find a noticable performance difference (mainly when scanning my hard drive for files though).
October 24, 2001 8:50:52 PM

Oh, I agree. You'll definitely notice the difference between 7200RPM and 5400RPM. I noticed a much quicker boot up, for one thing. That was obviously the first thing I noticed, so that stands out.

<font color=green>I post so you don't have to!
9/11 - RIP</font color=green>
October 25, 2001 4:13:17 AM

First of all, a standard PC has only a 32-bit PCI slot, providing 133MB/s max transfer speed. You don't need the super-expensive new stuff to fill that. I got a 3-channel SCSI RAID U2 LVD controller for only $100. I'm putting two INEXPENSIVE two year old U2 drives on each of two channels. Remember that a two year old SCSI drive has as much warrantee as a new IDE drive because they are warrenteed for 5 years instead of three!
My four older drives in Raid O will FILL the bandwidth of my PCI bus! And that's FULL TIME transfer rate, since each 80MB/s has a sustained rate of around 33MB/s. Plus I'm adding 64MB cache to the card!
The total cost of my drive system will be LESS than the cost of a U160 card with a SINGLE U160 DRIVE and will work MUCH faster!
What to do with the third channel? Put all my slower devices on it!

Back to you Tom...
October 25, 2001 4:58:34 AM

If money really is no moject and you really need the best available performance, then SCSI is the only way to go.


P.S. that guy who told u about 15k rpm drive is full o' crap. 15k drives are the best for acess times, seeks and transfer rates.

IDE, even IDE RAID, is for enthusasts.

so you will want a number of FAST SCSI drives, 5 or 6, 10k or 15k rpm. (if u use 10k rpm you will get greater capacity

then using a scsi controller you can run a RAID 3 or RAID 5 array... much more efficent and effective than RAID 0,1 or 0+1.
and the good thing about SCSI raid is that if you want more speed you can add more rives. IDE raid is usually limited by the number of IDE connectors it has.
so with raid 3 or 5 you have multiple redundant spanned disks... if you use 15k drives that system would rock!


Religious wars are 2 groups of people fighting over who has the best imaginary friend.
October 25, 2001 4:55:47 PM

Crash, you're my hero!

But I think you mean a 32-bit PCI slot, not a 32MegaByte PCI slot.

<font color=green>I post so you don't have to!
9/11 - RIP</font color=green>
October 25, 2001 6:11:06 PM

Level 0 is fastest. Level 1 is most secure. Level 3 and 5 are good for increased data integrety, but generating parity makes it a SLOW option. RAID 50 would be the best choice for someone who needs increased integrety with increased speed, but RAID 10 would be the best for anyone who wants the greatest speed with a simple backup cluster. Raid 1 and 10 ARE more secure than Raid 3, 5, 30, or 50, and RAID 10 IS faster than 3,5, 30, or 50.

Back to you Tom...
October 25, 2001 11:20:46 PM

argh! it hurts!
always have troubles sortin out which raid is which... finally know the diff between 0 1 and 1+0... but exactly how they do 3 & 5 is still a bit confusing...

but as the guy said, performance is everything and cost not an issue..
i suggest stack up the 36Gb 15k rpm seagates and go nuts!

Religious wars are 2 groups of people fighting over who has the best imaginary friend.
October 26, 2001 1:18:01 AM

Level 3 uses a separate parity drive. It's supposed to repair lost data on the fly, but at the expense of performance, caused by generating a parity bit. Similar to the performance loss from using ECC memory, but of course to a greater degree since hard drives are much slower. Level 5 does the same thing except it uses a separate parity segment on each drive. Level 3 and 5 drives, to the best of my knowlege, are sequential, when one fills up the other starts filling.
Level 30 and 50 use parity plus striping. This combination gives the performance benefits of level 0 with the performance deficits of level 3 or 5. Now to recap the other options:

Level 1 does not have parity, it does not check for lost data. But it does make an exact copy in case a drive fails. It has little affect on performance but protects you from a drive failure. It is mainly used for criticle applications such as storing expesive data. It is expensive because you only get the capacity of half the drives, since the other half are all backups.

Level 0 is striping. It allows you to access several drives simultaniously for increased performance. But if one drive fails, the whole cluster goes down. It is considered the best for high-performance non-criticle operations such as gaming.

Level 10 combines level 0 and 1 on two separate clusters, a primary and a backup. Each of these clusters is a level 0. It gives you very near Level 0 performance.


Back to you Tom...
October 26, 2001 1:21:33 AM

I have a really good solution for you. Instead of using two 15k RPM drives, use 4 10k RPM drives at half the size in Level 0. At about 30MB/s/drive you can get 120MB/s. And the smaller, slower drives are about half the price, the end result being twice as fast.

Back to you Tom...
Anonymous
a b G Storage
October 26, 2001 4:34:45 PM

Or get the new 6channel Promise SuperTrak100 and (4) IBM 60GXPs. You might end up maxing out the PCI bus (unless you are entirely pci 2.2 compliant) but the supertrak will let you go IDE RAID 5.

The 60GXPS have a listed throughput around 40MBs but I usually get around 36-38 when I'm testing mine. On my promise fastrak100 Raid0 array I get around 60MBs w/ 2 drives.

The cost savings with IDE raid would allow you to increase the # of drives. By using the 6channel card you get around the channel bandwidth problem.

In the ideal situation you could get a SCSI U320 raid controller and a few 15K drives but thats a few thousand dollars and IMHO not worth it unless you are running an enterprise level server. There are also alot of driver issues with scsi raid (I've only used 2 systems and both had Win2k issues)
Anonymous
a b G Storage
October 26, 2001 4:44:38 PM

As for RAID levels, here is what I recall. I hope its correct...

Raid 0 -- stripping. Max performance benefit but no data protection. Just splits the access acrossed multiple drives.

Raid 1 -- mirroring. Makes a realtime backup on the second drive. Must use even # of drives.

Raid 1+0 -- mirroring then stripping. (needs 4 drives) Takes a pair of mirrors and strips them.

Raid 0+1 -- stripped mirrors. (needs 4 drives) Takes a stripped array and mirrors it on a second stripped array.

Raid 3 -- (needs at least 3 drives) Spans the data acrossed all the drives but one. Stores parity information on 1 drive that allows recovery of any failed drives. (this is NOT the same parity as in RAM). Slower than Raid0 since the single partiy drive is a bottleneck.

Raid5 -- (needs 3+ drives) Spans the information across all the drives. Spans the parity information across all the drives. Removes the bottleneck of raid 3. Downside -- expensive controllers. Not quite as fast as RAID0 but offers FAR superior data protection.
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