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4disks RAID 0 and RAID 5 combination

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June 14, 2007 9:51:21 AM

Hi...
I'm planing to build me a new desktop with MB ASUS P5K-E (chipset P35+ICH9R) and 4xHDD (Western Digital SE 320GB 16MB SATA2 WD3200KS)

I've got some questions witch I wasn't able to fing on the web.
1. Is it possible to make cofiguration of disks like:

50% of 4 disks - RAID 0 (for Swapfile and work which needs performance like Video-editing or games)
50% of 4 disks - RAID 5 (for system and applications with the little safeness and performance of RAID5)


or do I need the full capacity of disks to have RAID 5

2. Are the disks which I choose OK? Can there be any HDD or is there some special HDD atribute which is for RAID 5 better advisable.

3. I didn't found on the web any performance comparison on different RAID configurations. Like what is real performance advantage between 1HDD, 2HDDxRAID0, 4HDDxRAID0, 4HDDxRAID5.
I know what should it be theoreticaly, but there is sure some HW performance expense/leak.

4. Should I consider RAID card because of CPU utilization (I'm planing 6700 Core2Duo). Or is there some REAL utilization at all, in comparisom to 1disk or 2disk RAID 0?
June 14, 2007 10:52:15 AM

Typically you cannot combine different types of RAID, although there are some ways it can be done you really would not gain anything from doing it. In your case I would get a RAID card that supports RAID 5 and configure all four drives in it. RAID 10 would almost give you what you are asking for by setting up the drives in striped pairs of RAID 0 but it really does not have that much of a advantage over RAID 5 other than it would not be hitting one drive really hard for parity.

I think going with a RAID controller that supports RAID 5 is your best bet and even several motherboards have it built in now. And no, there are not any special RAID drives, any drive can be configured as part of an array except of course something like a USB thumbdrive. :wink: The drives you chose are fine.

Hope this helps.
June 14, 2007 11:03:08 AM

Having 2 partitions on a disk and putting each one into a different RAID set will kill the performance, as the disk heads have to switch back and forth continually to act as 2 disks. Even then, only software RAID allows you to do RAID with partitions. RAID controllers require the whole disk to be used as a RAID component.

Picking a RAID level is always a compromise. Your best bet would be to get a quality RAID controller (not Adaptec, maybe LSI), that has a good enough processor to increase the write speed for RAID 5 so it isn't such an issue. You'd probably need to be looking at 8 port cards to get that kind of performance, but at least you'd be able to increase the size of the array later by adding more drives.

CPUs may be faster these days, but I'd still recommend a dedicated RAID controller (for RAID 5), as there is also a lot more data to work with, with much bigger hard drives, so it still can take a lot out of the CPU. Motherboard RAID controllers aren't good enough for RAID 5, as they offload all the parity calculations to the CPU. If they had hardware parity then the motherboards would cost a lot more, and have some much bigger chipset heatsinks.
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June 14, 2007 12:04:21 PM

I agree with Bumster and Polarity; mobo RAID-5 is a dog, so if you want RAID-5, get a dedicated RAID card.
If you want a RAID for data protection, mobo RAID-1 is fine. You lose the capacity of half your drives, but they're so big and cheap now that may not matter.
June 14, 2007 1:03:03 PM

Quote:
Typically you cannot combine different types of RAID, although there are some ways it can be done you really would not gain anything from doing it. In your case I would get a RAID card that supports RAID 5 and configure all four drives in it. RAID 10 would almost give you what you are asking for by setting up the drives in striped pairs of RAID 0 but it really does not have that much of a advantage over RAID 5 other than it would not be hitting one drive really hard for parity.


RAID 5 uses the equivalent of one drive for parity. In reality, the parity data is spread across all drives in the array. RAID 10 offers much better writes than a RAID 5 array, and is very noticeable.

Quote:
I think going with a RAID controller that supports RAID 5 is your best bet and even several motherboards have it built in now. And no, there are not any special RAID drives, any drive can be configured as part of an array except of course something like a USB thumbdrive. :wink: The drives you chose are fine.

Hope this helps.


Totally agreed. Integrate array controllers on desktop boards are a slouch.
June 14, 2007 1:16:30 PM

Agree... now I get it about having two partitions (Intel Matrix on ICH9R)...

So I'll use only RAID 5.
Question is, if a controller for 300$ is so much advantage against SW RAID on MOBO if its only for a desktop?

CPU utilization for parity disk is used all the time when using storage? or just for writing?


I've come on a new idea: What about to use

3 disks on RAID 0 for swap, video-edit, games (better performance than RAID5 with no CPU utilization for parity disk)
2 disks on RAID 1 for system, apps, data
June 14, 2007 4:34:56 PM

Quote:
Agree... now I get it about having two partitions (Intel Matrix on ICH9R)...

So I'll use only RAID 5.
Question is, if a controller for 300$ is so much advantage against SW RAID on MOBO if its only for a desktop?

CPU utilization for parity disk is used all the time when using storage? or just for writing?


I've come on a new idea: What about to use

3 disks on RAID 0 for swap, video-edit, games (better performance than RAID5 with no CPU utilization for parity disk)
2 disks on RAID 1 for system, apps, data


RAID 5 parity calculation is only used for writing, or if one of the drives fails. Read is the same as RAID 0 with a bit of overhead for skipping over the drive with parity for each stripe.

Some RAID 1 cards allow you to read alternate data blocks from each drive, giving slightly higher performance than a single drive, but not quite as much as RAID 0.

If you're really pushing for speed from RAID 5 then a dedicated controller is the way to go. Anything else will start eating into your CPU, so no RAID may be better if you want CPU to be fast, but aren't too bothered about disk speed. SATA sure is fast on its own so can be good in RAID 1 if you want some security.

Here are a few of read speeds for the RAIDs I've got:

5 disk RAID 5 U160 SCSI on dedicated LSI PERC3 PCI-X RAID 5 controller = 44MB/s (individual disks hit 20MB/s)
8 disk RAID 0 SATA 300 array on Highpoint 2220 PCI-X controller (software raid) = 102MB/s
2 disk RAID 1 ATA66 on G4 Mac onboard IDE controller using software RAID = 5MB/s
Single Maxtor SATA 150 drive = 52MB/s

I use gigabit ethernet, so the RAID0 in my fileserver is suited rather well to it's task at 102MB/s, even if it's not the fastest I could do, as the network tops out at around 90MB/s.

You could use the motherboard controller for RAID 0, as the CPU overhead is tiny for that RAID level, then instead of getting a dedicated controller you could make the RAID 1 using Raptors to make up for any performance loss from the single drive read speed. You don't need the big 150GB ones, even 72GB should be enough for sys and apps. Having less space for data files to build up is good practice, because it forces you to do back ups, then when the data is safely on DVD you can dump it onto the big RAID 0 and take advantage of the speed.

That's why I've got 2 60GB drives in RAID 1, and 8 320GB drives in RAID 0 instead of RAID 5. I've had 2 drives fail at the same time in the past, and losing several terabytes of stuff from a RAID 5 that hasn't been backed up is a lot worse than having to copy a huge amount of stuff back onto a failed RAID 0.
June 19, 2007 5:31:13 AM

Quote:
5 disk RAID 5 U160 SCSI on dedicated LSI PERC3 PCI-X RAID 5 controller = 44MB/s (individual disks hit 20MB/s)
8 disk RAID 0 SATA 300 array on Highpoint 2220 PCI-X controller (software raid) = 102MB/s
2 disk RAID 1 ATA66 on G4 Mac onboard IDE controller using software RAID = 5MB/s
Single Maxtor SATA 150 drive = 52MB/s


No offense but those speeds are terrible, I get ~120 MB/s on a 2 drive RAID0 and about 230 MB/s on a 5 disk RAID3

And to the OP, never do onboard RAID5...ever. RAID5 doesn't have much use on the desktop anyway, go RAID0 and use the extra as a backup, since RAID5 is no substitute for a backup anyway.
June 19, 2007 6:13:40 AM

Yeah I also get about 120mb/s using raid0 with 2x80gb seagate 7200.9 drives. Burst speed is around 325mb/s.
June 19, 2007 8:01:02 AM

Well the Highpoint is an example of a POS raid card, and a manufacturer never to go near. Their support is pathetic to say the least (It was the only 8 port card for a Mac when I got it).

Being in a 64bit 33mhz slot should only limit it so far, as a 4 drive RAID 0 on a Seritek card hit 194MB/s in the same slot in reviews.

I'm going to be moving the disks over to a PCI-e card from a decent manufacturer at some point, as there are better controllers onboard recent motherboards.


I could probably get more out of the RAID 5 on the PERC, but is's configured for security, not speed (I've seen people mention a 6x improvement when switching the cache policy).
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