RAID Controller

[koopkoop2]

Does anyone here own a RAID controller?

I am looking to buy one and I want some first hand opinions on how much of a performance gain I can expect.

Also, are onboard controllers that much worse then the PCI type?

[t3rry]

just get one of these

http://www.lacie.com/products/product.htm?id=10118

[rage2]

Originally posted by t3rry
just get one of these

http://www.lacie.com/products/product.htm?id=10118

t3rry, READ carefully before you post. You seem to be posting everywhere. He's looking for PERFORMANCE benefits, not CAPACITY.

Anyhow, onboard controllers are nice. They're somewhat basic in terms of functionality (raid0,1,0+1 only), but they do work ok.

By using RAID 0 on 2 drives, you're doubling the read and write performance, but without any redundancy. One drive goes, and poof, all the data's gone. RAID 0 on 4 drives with 4 dedicated channels is BLAZING fast.

RAID 1 mirror duplicates everything. Write speed doesn't change, but read speed is doubled on a 2 drive config. Huge waste of space (1/2 capacity of 2 drives usable)

RAID 0+1 mirrors and stripes. 4x the read performance, 2x the write performance, on a 4 drive 4 channel setup. I use this on my home machine using on board RAID. Works wicked, but again, huge waste of space.

RAID 5 is the best setup, which only the higher end RAID cards support. CPU usage is quite high if you use the software RAID5 setup (win2000 server, win2003). On a hardware RAID 5 card with onboard XOR engines, it's transparant. On a 4 drive (200gb each) setup, you'll get 600gb of usable space and only lose 200gb for redundancy. You'll get 3x the read performance, 3x the write performance. On a 8 drive setup, it's even more cost effective, 7x read/write improvement, again, only 200gb lost, with total capacity of 1.4TB.

[turboMiata]

Yah, but the problem with RAID 5 is the parity strip. When you are writing to the disk, having to compute and write parity actually degrades performance. That's why on high end RAID controllers, there lots of write-back cache on board the card. You'll also need battery backup to prevent corruption as a result of using this feature.

[rage2]

Originally posted by turboMiata
Yah, but the problem with RAID 5 is the parity strip. When you are writing to the disk, having to compute and write parity actually degrades performance. That's why on high end RAID controllers, there lots of write-back cache on board the card. You'll also need battery backup to prevent corruption as a result of using this feature.

That's why RAID5 cards have to be chosen wisely. The XOR engine's have to be powerful enough to sustain writing to 8 drives at once (or 4, or 6 depending on your configuration).

I've used software RAID 5 on 4 drives as a test, and the CPU usage on a P4 2.8ghz is fairly low, under 3% sustained. Performance was way better than the RAID 0+1 setup I had.

I'm looking at testing out the Promise SX6000 6 drive controller...

[tt398]

I use the Adaptec 3210S RAID controller with 14 SCSI drives (18 GByte each). I use RAID-1 so I dont loose data. Most home users dont wnt to spend this kind of money - the controller alone is $1K.

t.t.

[hampstor]

The other RAID level is RAID 50 (0+5).. a rather odd one where you stripe 2+ RAID5 arrays (a striped stripe with parity). You will need at least 6 drives to pull this one off.


Level/Minimum number of drives required

RAID0: 2 drives
RAID1: 2 drives
RAID5: 3 drives
RAID0+1/10: 4 drives
RAID50/0+5: 6 drives

If you want to learn more about RAID, you can always go to the adaptec site: http://www.adaptec.com/worldwide/pro...alk_about_raid

Check that site out or you can do like I did and tell staff when they ask me about RAID that it kills bugs dead

[spike98]

I just picked up 2 37gb WD raptors that i am going to run RAID 0


MMMMMMMMMMMMMMMMMMMMMMMMM 20 000 rpms

[Khyron]

Originally posted by tt398
I use the Adaptec 3210S RAID controller with 14 SCSI drives (18 GByte each). I use RAID-1 so I dont loose data. Most home users dont wnt to spend this kind of money - the controller alone is $1K.

t.t.

WTF - if you have 14 drives, are you sure you're just mirroring? That's wasting 7 drives. Why not go 5 and keep a drive as a spare?

Khyron

[rage2]

hehe I was wondering the same thing. RAID5 would make much more sense in his setup.

[tt398]

Originally posted by Khyron


WTF - if you have 14 drives, are you sure you're just mirroring? That's wasting 7 drives. Why not go 5 and keep a drive as a spare?

Khyron

My server uses dual Opteron CPUs - and is used for commercial purposes. That means I have a service level agreement (SLA) with my customer for uptime and data avialability. If I don't meet my SLA I dont get paid.

The 3210S is a dual channel LVD scsi controller that supports 14 scsi IDs on each channel. I put 7 scsi IDs (drives) on each channel to keep performance up.

On the first channel I use two scsi drives in RAID 1 for the operating system. The third drive is standalone - used for temp / tmp file systems and the swap filesystem. The other four drives are RAID O for applications. The second channel is used for application data storage - and is done in RAID5 - with one drive as a hot spare.