SCSI vs. IDE

[Hippie_Tech_Too]

I recently got into a debate over SCSI vs. IDE. Does anyone know what the difference in reliability for SCSI hard drives is compared to IDE hard drives? I honestly don't have much experience with SCSI hard drives since 99% of the computers I work on have IDE drives. The illusion that I get is that IDE are not as reliable as SCSI. However, I am basing this on the fact that I replace a lot more IDE drives than SCSI, but I don't work on many machines with SCSI. I couldn't find any information on the web about the difference in reliability other than MTBF [mean time between failures (?)]. The reason I'm asking is that I have a client that needs a server setup with RAID 5 (which you can do with SCSI or IDE). The difference in price is almost $2000.00 extra cost for the SCSI setup. I didn't see any problem with using an IDE setup since they will also have a tape backup for their sensitive data. My stance in the debate was that the IDE server would have 2 forms of fault tolerance, RAID 5 and a tape backup. My friend insisted that SCSI were much more reliable (which I can't refute for lack of information) and there was a possibility of losing 2 IDE drives at the same time. Now I realize there is that possibility, but the odds are extremely unlikely that 2 drives would fail at the exact same time and even if they did that's what the tape backup is for. I know the customer is going to balk at the higher price of SCSI, but my friend thinks that I should just work harder to convince the customer to go SCSI anyway. Why? <img src="confused.gif" border="0">

[DonJ]

Concerning which is more reliable, they are probably about the same...no stats here to go by, just expereience.
One of the main advantage of using SCSI over IDE is the speed or Data Transfer Rate. Single-Ended SCSI can typically handle up to 10MB per second while Fast/Wide SCSI can handle up to 20MB per second.

For IDE:
PIO Mode 0
3.33 MB per second;
PIO Mode 1
5.22 MB per second;
PIO Mode 2
8.33 MB per second;
PIO Mode 3
11.1 MB per second;
PIO Mode 4
16.7 MB per second;
DMA Mode 0
4.2 MB per second;
DMA Mode 1
13.3 MB per second;
DMA Mode 2
16.7 MB per second.
NOTE: If you install two IDE devices with different data transfer rates on the same data cable, the data transfer rate of the faster IDE device will be reduced to match the rate of the slower IDE device.

These stats were taken from HP's website...hope it helps out somewhat. Let us know how it goes.

[Hippie_Tech_Too]

The drives in question are:

SCSI drives: Seagate 15K RPM 18GB (Total of 4 drives = 72GB)
I realize that RAID 5 will eat some of the usable space.
IDE Drives: Seagate 7200RPM 40GB (Total of 3 drives = 120GB)
I checked the price of having 3 36GB SCSI drives. It's even more expensive. The SCSI drives are the Ultra160 flavor and the IDE drives are ATA-100 drives. I do realize the access times will be lower on the SCSI drives because of the latency at 15K RPM, but the throughput should be about the same. They are going to be using the server as a data storage machine more than anything else. They have a auto-mechanic software package that comes on DVD that they load onto the hard drive so everyone can access the information from the DVD disks. The difference in speed between SCSI and IDE is a non-issue for what they are using it for. Thanks.

[DonJ]

In case you haven't already done so, check out <a href="http://www.seagate.com/" target="_blank">http://www.seagate.com/</a>
You will find all kinds of specs, installation guides, etc. The MTBF is what most people use as a bench mark for reliability.

[Mayhem]

If you are looking at a server for more than a few workstations I would go with SCSI. Access times are faster and the are designed to handle multiple requests. Also transfer rates are at sustained speeds.

Ide has a little trouble with muliple requests and transfer rates are always listed as Burst, the tend to slow down on large files.

On the reliability side. I have dealt with very few client machines running SCSI drives. In my own experience, I have a pair of Seagate SCSI II 9 GB drives in one of my servers. They have been fault free for 4 years and I don't forsee any failures in the near future. I have some WD IDE 6-8 GB drives as old and they are in just as good shape as the SCSI's.

It's more a matter of work load. On my small network none of the drives work that hard. On a large corperate network they will work hard and the SCSI drives are better designed to handle thatkind of workload. IDE is designed for workstations and home PC's that don't work as hard.

[silencio]

Go with SCSI for the server. The performance of SCSI in a server environment is untouchable by IDE. Don't get me wrong, I'm a big fan of IDE RAID but it has it's place.

Good example, I had a DC running on mirrored IDE drives on an Abit VP6 with the Highpoint RAID controller.

Drive 1 went bad and the RAID controller failed it. After a reboot the RAID controller decided that it wasn't bad after and recognized it. So, this drive now shows up in Windows 2000 as drive number two. Now, don't ask me how windows 2000 decides what drive letter a drive gets. I've seen drives sandwiched so that drive 0 is C: and E: and drive two is drive D: and F: and I've seen them as concurrent drive letters. Either way, Windows takes this (bad) drive and sandwiches it into my logical drive setup. Remember, this drive was a mirror and is supposed to have all the same data and, I initially had 3 partitions on the "single" drive.

So, now I have 6 drive letters, 3 of which are bad and can't be written to. Windows magically adjusts and moves my pagefile to an unwrittable drive and I can't logon (no pagefile error and no services will start). I shut down, pull the drive, reboot, can't logon, no pagefile. Windows doesn't magically adjust back. I reboot in safe mode, won't work. I reboot in directory restore mode, won't work, no pagefile. I do a parallel install and restore the last full backup (which should hvae the correct pagefile drive letter assignments) and I get the same error. After a few more hours of chkdsk and trying to find pagefile settings in the DOS version of the registry I said screw it. I didn't have a good drive to replace the bad one and I wasn't going shopping. The machine wasn't in a production environment anyway but I hated to give up.

Moral of the story, when a high end SCSI RAID controller fails a drive, it stays failed. There are number of other little details like that that have been found in the years of R&D of SCSI RAID controllers. For that reason alone I go with SCSI.

sorry for the long post..

[xt477]

Sorry if these are not the exact drives I forgot to quote you But should give you an idea.

st373405lw has a mtbf of 1,200,000

st380021a has a mtbf of 600,000

[korpse]

The main issue is speed. SCSI is faster than IDE (some of the spin rates are crazy ex: 15K RPMs = much faster access times). As far as reliability, they are about the same....thats what RAID 5 is for!