Data Loss Risk: RAID 1 vs. RAID 5

[bjbgraphics]

I am implementing a RAID array on my server.
I have narrowed it down to two options:

RAID 5 - 4 x 80 GB HDs
3ware 7506-4LP KIT PCI IDE Controller Card - Retail
Maxtor DiamondMax 10 6L080P0 80GB 7200 RPM IDE Ultra ATA133 Hard Drive - OEM

Price: $449.99
Total available HD: 240 GB

OR

RAID 1 - 2 x 300 GB HDs
3ware 7006-2 PCI 2.2 compliant 32-bit/66MHz bus master IDE RAID Card - Retail
Maxtor MaxLine III 7L300R0 300GB 7200 RPM IDE Ultra ATA133 Hard Drive - OEM

Price: $371.99
Total available HD: 300 GB

It is my understanding that if more than one hard drive dies on a RAID 5 you lose everything. Isn't this the same risk with RAID 1?

Thus, does it not make more sense to go with the RAID 1 option as it is cheaper, provides more hd space, and provides the same level of protection as RAID 5? What data loss security would I gain from the RAID 5 setup?

Thanks!
BJB

[John64]

i thought you could only have drives in multiples of 3 for raid 5, but i am probably wrong

Keep in mind as well that you need a very good controller to use RAID5 properly.

Raid 5 outperforms Raid 1.

If more than one drive fails in a raid1, both your drives are dead, so nothing works.

In a raid 5, you dont get the full 4x80 to my knowledge, as the parity information is taking up at least 1x80.

[pointreyes]

I have run 4x120 with a 5th drive as a hot global spare for a RAID 5 configuration.
Had two drives fail on me at the same time and lost no data - it was due to having the 5th drive. Using 4 disks for the RAID5 is always better than 3 disks. It also makes it easier to determine total space since 4x120 would equate to 3x120 disk space. Note that I usually prefer RAID1 for the OS and programs and RAID5 for the data. I have seen too times in the past of others that used RAID5 for their single solution and end up losing the ability to recover the OS.

Currently, due to budget constraints I have to run a 4 disk RAID5 with no hot spare and my OS is running on a single drive. I'm just making sure that I image backup the OS since it's not that big of deal to me anymore if the OS drive fails on the file server.

[CYCLOPS]

Well ... up until recently, I subscribed to the Raid idea for speed (see Intel white papers on ICH5,6,7 for the technical advantage.

I had my machines set up with both Raid0 and Raid 0+1.

The majority of backup software out there just has problems with Raid in any form!

On the Raid0+1 machine, (Highpoint), none of the software would work correctly with it. When I had a drive crap out, the "rebuild array" failed miserably and that machine went back to individual IDE drives.

On a Raid0 machine, (Stupid me) didn't test a restore with Acronis.
I made a fresh image, as it read everything just fine and burned an image just fine, had a major malfunction after the reboot. Ran a restore from Acronis successfully ... yeah! it successfully restored the image to 1 of 2 drives and blew the array. Of course, the image that I had just made was on the array... That machine is now single SATA drives.

As far as the speed ... I really don't see any difference in performance.
I have decided to stay away from Raid and stick with image backups I know restore successfully. I would rather add drives to store the images than lose the whole thing in one fell swoop again.

[pointreyes]

Performance is an issue with RAID5. You might want to look at the difference in speed between the 8-port and the 4-port 3Ware controller cards. I was surprised to see that there is a difference between 4 and 8 port cards. That was back in the days of the 74xx IDE card series. Switched to SATA and like the speed of 80~100Meg per second on my hot-swappable RAID5.

[bjbgraphics]

John64

I believe you only need a minimum of 3 drives for RAID 5, and you can add more as your controller allows.

The 7506-4LP 3ware controller I linked has dedicated hardware (as does the 7006-2) and should handle the RAID 5 array fine. Performance is not my chief concern.

I don't think RAID 5 outperforms RAID 1... it seems to depend on the controller mostly, but RAID 5 requires a lot more processing with all the parity stuff.

Both RAID 1 and RAID 5 will have total data loss if more than one HD dies. That is why I question what benefit RAID 5 would have for me.

Right, RAID 5 available space is calculated as: (Number of HDs - 1)HD Capacity

pointreyes

I could run RAID 5 - 3 x 80 GB HDs with 1 x 80 GB Hd spare but then my available space goes down to 160 GB, it still costs $449.99, and during the time the RAID 5 array is being rebuilt... if another drive goes I lose it all.

Still seems to me the RAID 1 setup is the better choice.

CYCLOPS

I am not really interested in performance. I will be running the OS on a separate drive and imaging it. RAID 0 just seems like a bad idea overall and definitely isn't a consideration for what I need.

Thanks for the replies!
BJB

[John64]

Raid 1 offers Zero performance enhancements, i was under the impression that Raid 5 offered modest performance benefits with a good controller.

Raid 1 offers total data integrity, and fault tolerance, redunant to the number of times you have hard disks. Raid 5 with 3 disks offers 1 disk of redundancy i beleive

[pointreyes]

Originally Posted by BJB

pointreyes

I could run RAID 5 - 3 x 80 GB HDs with 1 x 80 GB Hd spare but then my available space goes down to 160 GB, it still costs $449.99, and during the time the RAID 5 array is being rebuilt... if another drive goes I lose it all.

Still seems to me the RAID 1 setup is the better choice.

That's why I mentioned 4 disks plus hot spare. It does not do much good to go with 3 disks plus hot spare. Sorry, I keep forgetting that you are using a 4-port controller. My 8-port controller handled the lost of two drives very well and it was built to accomodate for fast r/w operations during a rebuild. Considering you are looking at a 3Ware, I would expect the same performance. The good thing is that the 3Ware is a true hardware controller so the load of the RAID5 is done off the controller's processor chip instead of being offloaded unto the motherboard's processor(s) (this is a common reason why many of the less expensive RAID5 controllers don't handle the load very well).

[Protoplasm72]

If you're not interested in performance then raid 1 is the way to go. To dust off my statistics hat, you are more likely to have 2 out 4 hard drives fail at the same time then 2 out of 2 fail. Think of it this way... If 1 hard drive fails in a raid5 setup you now have 3 hard drives where any failure in any of them causes you to lose everything. That'd be worse then a raid0 with 2 disks

[bjbgraphics]

Understood. Is there a reason you wouldn't setup a RAID 1 with two hot spares? The 4 port controller could have 2 HDs for the RAID 1 array, and then 2 hot spares. This would offer just as much fault tolerance with less expense, wouldn't it?

BJB

Originally Posted by pointreyes

That's why I mentioned 4 disks plus hot spare. It does not do much good to go with 3 disks plus hot spare. Sorry, I keep forgetting that you are using a 4-port controller. My 8-port controller handled the lost of two drives very well and it was built to accomodate for fast r/w operations during a rebuild. Considering you are looking at a 3Ware, I would expect the same performance. The good thing is that the 3Ware is a true hardware controller so the load of the RAID5 is done off the controller's processor chip instead of being offloaded unto the motherboard's processor(s) (this is a common reason why many of the less expensive RAID5 controllers don't handle the load very well).

[Bofinn]

RAID-10.

Combining RAID-0 and RAID-1 is often referred
to as RAID-10, which offers higher performance than
RAID-1 but at a much higher cost. There are two
subtypes: In RAID-0+1, data is organized as stripes across
multiple disks, and then the striped disk sets are
mirrored. In RAID-1+0, the data is mirrored and the
mirrors are striped.

[bjbgraphics]

Right, that is my thinking as well. It does not seem that RAID 5 offers any fault tolerance advantage over RAID 1. The advantages seem to lie in performance and HD space efficiency which I doubt my network and server would gain any real benefit from. At least, not proportionate to the amount of money needed to implement it.

BJB

Originally Posted by Protoplasm72

If you're not interested in performance then raid 1 is the way to go. To dust off my statistics hat, you are more likely to have 2 out 4 hard drives fail at the same time then 2 out of 2 fail. Think of it this way... If 1 hard drive fails in a raid5 setup you now have 3 hard drives where any failure in any of them causes you to lose everything. That'd be worse then a raid0 with 2 disks

[pointreyes]

Originally Posted by BJB

Understood. Is there a reason you wouldn't setup a RAID 1 with two hot spares? The 4 port controller could have 2 HDs for the RAID 1 array, and then 2 hot spares. This would offer just as much fault tolerance with less expense, wouldn't it?

BJB

That seems weird to me. You would only see one drive out of the four and I'm not sure if it would work. Sounds like a mirror in a mirror. You have various options available to you but one that I like would be RAID1 with one hot spare and then an external drive for backup of the data and image backups of the OS.

[pointreyes]

Originally Posted by BJB

Right, that is my thinking as well. It does not seem that RAID 5 offers any fault tolerance advantage over RAID 1. The advantages seem to lie in performance and HD space efficiency which I doubt my network and server would gain any real benefit from. At least, not proportionate to the amount of money needed to implement it.

BJB

As I stressed before, I see RAID 5 good for data. If you must install the OS and programs on the same RAID configuration then I cannot recommend RAID 5.

[h20-ski]

Having built my 8 dik Raid 5, Raid 5 on 4 disks does not allow Raid 5 to shine as far as reduncy and space. A two disk RAID 1 would be better. As far as which to run, which one would allow you to upgrade the most, ie add another hard drive or put a bigger one in.