RAID3 with 2 different speed HDD's

Maxpv

Hey guys,

I've never used a RAID setup, so I'm gonig to explain what I'm trying to do in detail.

I have 2x150GB 10k RPM raptors, and a 300GB 7.2k RPM drive. This will be a software RAID. What I want to do is this:

Stripe my data across the 2x150GB raptors for speed.
Keep a mirror, or some other way of recovering my data, on the 300GB drive.

From what I understand, this is a RAID3 setup. Would I be able to do this with 2 different speed hard drives?

Thanks for your help guys, got a lot of help with my build from you guys.

roast

Blazr wrote: »

Hey guys,

I've never used a RAID setup, so I'm gonig to explain what I'm trying to do in detail.

I have 2x150GB 10k RPM raptors, and a 300GB 7.2k RPM drive. This will be a software RAID. What I want to do is this:

Stripe my data across the 2x150GB raptors for speed.
Keep a mirror, or some other way of recovering my data, on the 300GB drive.

From what I understand, this is a RAID3 setup. Would I be able to do this with 2 different speed hard drives?

Thanks for your help guys, got a lot of help with my build from you guys.

Its a very good question. I've worked on several RAID arrays in the past, but have never come across an array like the one you're describing.
To be honest, I don't believe it is possible.
First off, its RAID 0+1 that you want. Heres a description pulled from wiki:

RAID 0+1: striped sets in a mirrored set ( minimum four disks; even number of disks) provides fault tolerance and improved performance but increases complexity.
The key difference from RAID 1+0 is that RAID 0+1 creates a second striped set to mirror a primary striped set. The array continues to operate with one or more drives failed in the same mirror set, but if drives fail on both sides of the mirror the data on the RAID system is lost.

Its an easy system to make, but theres no way to make the third disk act as a mirror for the first two. Speed (10k vs 7.2k rpm) doesn't technically matter in a RAID array (although, undoubtedly it is preferable to have matched speeds/disks) its actually the capacity that matters. In this case, 300gb wouldn't work as a mirror for a striped pair of 150gb disks. You would have to have a second pair of 150gb disks to act as the mirror in this array. In theory, the second pair could still be 7.2k rpm disks.

I hope this clears it up for you, and if anyone else has actually come across an array similar to this, feel free to correct me.

Cheers,
Mick.

Maj Malfunction

This is not what you will get.

RAID0 with the two raptors will give you speed alright. Moving to RAID3 with the 7.2k rpm disks will degrade the overall performance of the 2 x Raptors.

If its speed and security you want then I would use Raid1 (mirror) with the two Raptors. 1 x 10k rpm raptor is as fast as raid 0 using a pair of 7.5k rpm disks, benchmarks verify this.

I gather your not planning on running RAID3 on Windows? AFAIK its not supported natively, so I assume your running FreeBSD? (http://en.wikipedia.org/wiki/RAID)

IMO I'd setup the OS on the 300GB drive and store all my critical files on the RAID1 (2 x 150GB Raptors).

Other things to consider is RAID array rebuild times for a disk failure. I know my RAID5 array if it fails will take over 80 hours to rebuild the container (Its over 2.5TB)!! RAID 1 recovery is simple and fast, take out the failed drive chuck it in the bin and put in the new drive and your back up and running.

Software RAID is going to shove all the work onto your CPU, so if your using this rig for gaming, you may suffer a performance hit.

BostonB

What do you need the speed for? I'm not convinced that any speed gains are worth the hassle of a RAID set up, when you could replace it all with a SSD use the other disks for storage/backup.

Maj Malfunction

BostonB wrote: »

What do you need the speed for? I'm not convinced that any speed gains are worth the hassle of a RAID set up, when you could replace it all with a SSD use the other disks for storage/backup.

There is alot to be said for KISS

Keep
It
Simple
Stupid

Then there is less to go wrong! :-)

BaconZombie

RAID IS NOT A BACKUP SOLUTION!!!!!!!


Best to Mirror the two 2x150Gb and then if put the 300Gb in a caddy or mount it but leave it disconnected { both the SATA and power }.

Then once a day/week/month/Q reconnect it and backup ALL your data to it.
When finished disconnect it again.

This is by no ways 100% safe since the PSU could blow all three or a controller error could CRC everything.

Blazr wrote: »

Hey guys,

I've never used a RAID setup, so I'm gonig to explain what I'm trying to do in detail.

I have 2x150GB 10k RPM raptors, and a 300GB 7.2k RPM drive. This will be a software RAID. What I want to do is this:

Stripe my data across the 2x150GB raptors for speed.
Keep a mirror, or some other way of recovering my data, on the 300GB drive.

From what I understand, this is a RAID3 setup. Would I be able to do this with 2 different speed hard drives?

Thanks for your help guys, got a lot of help with my build from you guys.

Monotype

RAID 3 is similar to raid 5 but you have one disk with parity rather than it spread across all drives. You would need drives all the same (or all drives will be adjusted to the lowest).

In my opinion - RAID-0 (stripe) the two raptors for the speed. Then backup either internally or externally (better for reasons stated by BaconZombie) to the 300GB drive.

Maxpv

Darn it, I just bought the drives without checking up on this thread.

I'll explain fully what I want to do and see if anyone can point me in the direction of a way of accomplishing it.

Here is what I now have:
3x 160GB Velociraptors
640GB 7200RPM HDD
1TB 7200RM HDD

What I want to do is keep my OS and applications on the velociraptors, I'd like to have them in a RAID0 or similiar for performance.

As I'd be using the 3 velociraptors for speed and not redundancy, I'd like to have a copy of my data, or some sort of way of restoring it if a velociraptor fails, on the 640GB drive, as I do not want to loose all my data if one of the raptors dies on me.

The 1TB is for all my music and stuff like that. I really don't care about performance or redundancy for this one.

I'm running Linux and would like to use a software RAID setup, however if I have to get a RAID controller, thats no problem.

Anyone have any suggestions for what I should do to achieve this?

Also, for those asking why I don't get a SSD instead, its because I got all these drives for 170euro, I don't think you'll get a good 480GB SSD with a backup HDD and a 1TB HDD for that!

And by the way, thanks a lot for the help guys, had a good read but I don't think these solutions do what I want. Thanks a lot for helping, I learned a lot about RAID setups from it.



EDIT:

Here are some of my computers specs if it helps:
AMD Phenom X6 1090t
Asus Crosshair IV Formula

BostonB

Blazr wrote: »

Also, for those asking why I don't get a SSD instead, its because I got all these drives for 170euro, I don't think you'll get a good 480GB SSD with a backup HDD and a 1TB HDD for that!...

Well theres hybrid drives.
http://www.anandtech.com/show/3734/seagates-momentus-xt-review-finally-a-good-hybrid-hdd

Maj Malfunction

You have a nice motherboard there

http://uk.asus.com/product.aspx?P_ID=kPGmtxee5RsQVsXG&templete=2

Good news is you mobo supports onboard RAID, this gives you some options. Hardware RAID will be faster than software RAID. Reading the manual for your mobo you can support RAID 0,RAID 1,RAID 5 & RAID 10

You have 3x 160GB Velociraptors. You want speed and not redundancy... but dont want to lose any data if a Velociraptor fails... but if it does fail you want to be able to recover the loss (so really you do want redundancy)

Go with 3x 160GB Velociraptors in RAID 5

You get speed and redundancy. This will give you 320GB of storage capacity. If one drive fails you can swap out the faulty drive without data loss (all going well).

You can keep a backup of the RAID array to your 640GB drive just in case anything really bad happens!

Your 1TB drive for everything else.

No need for software RAID, less hassle... Oh and good luck! :-)

Maxpv

Maj Malfunction wrote: »

You have a nice motherboard there

Thanks, I actually got it for free because of a mistake a retailer made

Maj Malfunction wrote: »

Go with 3x 160GB Velociraptors in RAID 5

This was my original plan, but I actually read online that RAID0 is much much faster than RAID5 due to all the extra parity writes. As far as I remember, it was only slightly faster than a non-raid setup. Correct me if I'm wrong as I just Googled it and actually now can't find anything to back that up.

Does anyone actually know if the performance between RAID0 and RAID5 is much different? If its only a small bit slower, I'll go with what Maj Malfunction suggested and put RAID5 on the velociraptors

Monotype

RAID 5 will definitely be slower as it has extra to write and also has to calculate parity. With a good processor, you shouldn't notice the extra CPU load. Read speeds on RAID 5 is generally good but don't forget that you are sacrificing a hard drive space too.

Maj Malfunction

In real terms I don't think you'll notice the speed differences between the two types of RAID in day to day use. The OP has got 3 very fast drives which will deliver the speed requirements anyway

Maxpv

Ok, Im now considering using a RAID5 setup, but I really cant see why its not possible to keep the parity data on a seperate, slower drive so I wont loose any precious velociraptor space. I really dont see the point keeping parity data on a really fast drive, why isnt it possible to put the parity data on a slow, seperate drive?

Thanks a lot for your help guys, I really appreciate it. I think Ill go with a RAID5 configuration.

Monotype

It's not possible really because it's calculating the parity while it's writing. It's not a backup that runs in the background that catches up with today's files.