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RAID 5 Question

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drakanious

n00b
Joined
Dec 18, 2006
Messages
13
I've looked around the internet for quite some time and cannot find an answer to my question: How does performance scale with RAID 5? And more specifically: Performance-wise, how would a 750GB 4 disk RAID 5 array compare to a 3 disk 640 GB one?

I know there are a lot of smart people here who can help me out on this one. :D

Thanks guys
 
The more spindles (drives) the better the performace.
I never recommend using host based RAID5 however.
Get a RAID controller and offload the work from the CPU.
 
Using what disks? What controller? Doing what with the array?
 
I'm rather fond of my RAID 5 setup. I haven't done any performance tests but the disk access seems really fast so I can't complain. HD Tach and IO Meter don't seem to like Vista x64.

I'm using an LSI MegaRAID 8308ELP PCIe x4 SAS/SATA Controller
I have 4 Western Digital Raptor 150GB drives in RAID 5 and it's quite nice. :cool:
 
Firstly, I'm sorry if any of these questions have been convered in another thread(s).

gigabyte1024 said:
The more spindles (drives) the better the performace.
I never recommend using host based RAID5 however.
Get a RAID controller and offload the work from the CPU.
Click to expand...

Are you recommending a controller with a parity (XOR) accelerator? Would there be any benefit to using an add-in card that doesn't have a dedicated parity processor? (Or do all add-in cards have that feature and I am mistaken?) Also, because parity is only calculated when data is written to the array, wouldn't the extra load on the processor be relatively neglible in a gaming environment (which is how I plan to use it, primarily)?

For reference, the 250GB HDD I'm looking at is a WD Caviar SE16 http://www.newegg.com/product/product.asp?item=N82E16822144701 and the 320 is a Seagate Barracuda 7200.10 : http://www.newegg.com/Product/Product.aspx?Item=N82E16822148140

I guess my original question is more along the lines of which array would be more efficient in terms of price per capacity per performance? (That is, is it worth the extra $40 for another 110 GB + performance?)

I've been seriously considering getting a RAID controller because I'm using a 680i which (as you may know) has a known problem with RAID and I rather avoid the whole situation.

Thanks
 
drakanious said:
Are you recommending a controller with a parity (XOR) accelerator?
Click to expand...

A good (aka expensive) controller will outperform a software solution. A crappy controller with dedicated IO processor may perform worse than software.

Would there be any benefit to using an add-in card that doesn't have a dedicated parity processor?
Click to expand...
Benefit with respect to what? Usually you can get a couple of more ports.

Also, because parity is only calculated when data is written to the array, wouldn't the extra load on the processor be relatively negligible in a gaming environment (which is how I plan to use it, primarily)?
Click to expand...
The processor load isn't the problem. The problem is that small writes require a lot of I/O interaction to be processed: If you are writing less than Stripe_size * (Number_of_Stripes-1) bytes, the write will be performed, followed by a read of the complete stripe, the parity calculation and then another write to adjust the parity.

I am not sure if gaming will benefit much from the increased reading STR that RAID-5 can offer.
 
drizzt81 said:
Benefit with respect to what? Usually you can get a couple of more ports.
Click to expand...

I meant instead of using the onboard RAID.

drizzt81 said:
The processor load isn't the problem. The problem is that small writes require a lot of I/O interaction to be processed: If you are writing less than Stripe_size * (Number_of_Stripes-1) bytes, the write will be performed, followed by a read of the complete stripe, the parity calculation and then another write to adjust the parity.
Click to expand...

Thank you, the clears things up quite a bit.

drizzt81 said:
I am not sure if gaming will benefit much from the increased reading STR that RAID-5 can offer.
Click to expand...

I was considering it for its cheap (disk-wise) fault tolerance, mostly, because I have a lot of media that I want safe.

At this point, I'm thinking it would be easiest to just save the money that I'd spend on a good RAID card, and instead buy 4 drives and just put them into a RAID 1+0 array. Any suggestions, in particular, if I budget $300 on this little project?

Thanks again.
 
drakanious said:
buy 4 drives and just put them into a RAID 1+0 array.
Click to expand...
Put more money in? :p The cheapest I can find 320 gig disks is $80, and I'd rather not buy disks from Newegg. That'd be over $300 for 4 disks, not even counting the controller.

Would you be planning to add more disks later, or is 4 the most you'd be likely to have?
 
drizzt81 said:
you're welcome.


RAID is not going to make your media safe. Not in the least bit.
Click to expand...

What do you mean? Are you saying redundancy doesn't give you any extra peace of mind vs. no redundancy at all?

Well, I'll tell you that from my experience (which is a long time of using computers to do stupid things before I became more aware of security, such as downloading game crack executables from fishy sites), data loss due to data corruption and viruses have been the least of my concerns on a hard drive, as well as data loss due to accidentally deleting files (which I can't remember doing for as long as I know). Data loss due to floods, fires, have also been of little concern. What I do see from other people all the time are hard drives dying (even though I've been lucky not to have any hard drives die on me yet).
 
First off, don't look at non RE drives from WD for RAID 5. Look up the TLER issue to see why. Either use a different brand, or get the RE drives.

Second, RAID is not backup, nor is backup RAID. RAID's only purpose is to increase uptime not to keep your data safe. Backups are to keep your data safe, not to increase uptime.
 
Cyrilix said:
What do you mean? Are you saying redundancy doesn't give you any extra peace of mind vs. no redundancy at all?
Click to expand...
yup, that pretty much sums it up.
Cyrilix said:
Well, I'll tell you that from my experience (which is a long time of using computers to do stupid things before I became more aware of security, such as downloading game crack executables from fishy sites), data loss due to data corruption and viruses have been the least of my concerns on a hard drive, as well as data loss due to accidentally deleting files (which I can't remember doing for as long as I know). Data loss due to floods, fires, have also been of little concern. What I do see from other people all the time are hard drives dying (even though I've been lucky not to have any hard drives die on me yet).
Click to expand...
That may be true for yourself. Given the posts I read on this forum, I would say that user error is most likely the greatest threat to data there is. As such, I feel that it is necessary to explain to people that RAID-1/5/10 is barely any safer than running just a plain disk.

edit:
WTF? My storage drive just got corrupted after a graceful restart!(PC restarts, partition info is lost)
Drive suddenly unformatted?
External Hard drive, encrypted mp3s! (user cannot retrieve data, thanks for encryption)
*Sigh* Lesson learned (cut & paste goes wrong)
 
Hmm... I see what you mean, but I'm still not entirely convinced. Nevertheless, time will tell. :)
 
drizzt81 said:
RAID is not going to make your media safe. Not in the least bit.
Click to expand...

QFT - If you have important information having a seperate copy of said information is the only true backup and the only way to ensure that it is safe.

Get an external hard drive or NAS and keep two seperate copies.
RAID != backup.
 
protias said:
I see my post made it on there. Anyway, yes Raid is no safer from single disks. What is to say your PSU doesn't go *boom* and take everything with it?

But now, we are just beating the dead horse..
Click to expand...

I guess we now need RAIP (Redundant Array of Independent PSUs), huh? :p
 
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