RAID - couple of basic questions

[GasX]

I have a spare 30GB 5400rpm drive laying around and a RAID Mobo on its way. If I get a matching HDD and go with a RAID set-up(striping) am I going to see a drastic increase in speed? How closely do you have to match HDDs? same size? same model?
Thanks in advance.

 

[CAMS]

"am I going to see a drastic increase in speed?"

Not by buying another 30GB 5400rpm. You could see a better increase by using a single 7200rpm on its own eg: Maxtor viper.

RAID 0 striping is faster at moving/working with large files eg: photo/video editing and databases. If you are not doing that then RAID 0 will show little benefit.

Yes its best to match HDrives for RAID 0 eg: 20gb + 40gb = 40gb total and it will run as fast as the slowest drive. Raid 0 offers no redundancy so if one Hdrive fails all data is lost.

 

[miken]

RAID 0 in IDE will have small speed gains, but you have to go to SCSI RAID to notice anything. IDE RAID for speed is a waste of money, IDE RAID for redundancy is smart.

5400 vs 7200 drives really is based on the HD manufacturer, some 5400 drives are faster than 7200's.

 

[LocalHero]

What CAMS are describing is a combination of volume set and raid 0.

Volume set is when you have 2 drives (can have different size) and make them to one drive. This will make your capacity drive 1+drive 2, Your speed will be either drive 1's speed or drive 2's speed depending on where on the disk you are reading. The thing with volume set is that the data is stored so that the first sector on the "virtual" disc will be on the first disc. The second sector is also on the first disc. and so it goes until disc 1 doesnt have any sectors left. Then it will continue on disc 2.

Raid 0 on the other hand is using another tecnic. This will require that the discs are the same size. Otherways it can only use the amount of space that the smalest dics has. Of course this depends on how your raid card/software works. raid 0 uses this teknik. It devides the disks into chunks of a certen size, lets say 32kb. Chunk 1 will be on disk 1, beloved patriot 2 on disk 2, chunk 3 on disk 1, chunk 4 on disk 2 etc etc. If you read the sectors on the "virtual" disc you will then read from disk 1 and then disk 2, disk 1 etc etc. This will increase your speed to in theory the speed of your slowest disk X 2. I have set up an raid 0 system in linux and im very close to 2x, 1.8 i get overall . Why this works is cause when you raed a sector on the disc the next sector you will read is probably the sector after that. With all the caching mechanics in both harddrive/disk controller etc you will have a virtual effect that the discs are actually reading data at the same time.

Hope you get something out of this.
/Alexander

 

[MichaelD]

Granted, benchmarks aren't everything, but here's mine from my new system (see the whole thread HERE )


SANDRA 2002 Standard

CPU: ALU 4236/FPU 2118 PR rating: 2246
Multimedia: Int 8400/ Floating pt. 9709
Memory Bandwith: Int buf 2019MB/s Float buf 1923MB/s

Drive Benchmark: 37,350
Buf read: 55MB/s
Seq read: 58MB/s
Rand read: 6MB/s

Buf wrt: 45MB/s
Seq wrt: 47MB/s
Ran wrt: 10MB/s

Access time: 9ms


Winbench99

CPU Mark: 142
FPU Winmark: 8400
Business Disk: 9550
Highend Disk: 24000

Disk benchmark: Beginning: 66,660 End: 45,800
Access time: 13.5ms CPU Utilization: 2.17



The same HDs run by themselves get about 65% of the scores that two drives get when RAID 0'd. Nuff said. IDE RAID 0 Is not a "waste of time". It's your equipment, you run it the way you want to. For me, it's more than worth the extra hassle to set it up and make regular backups. I wouldn't bother, however, getting another 5400 rpm drive to do RAID 0. If you do it, do it right. Get two IDENTICAL 7200 rpm HDs.