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Raid 1 vs. Raid 5

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November 10, 2011 6:48:41 AM

Hello, am planning to run Raid 1 or 5 and not sure what the decision points should be. Having discussed Raid with senior colleagues it appears that religion may have bearing on the correct choice.

What are the pros and cons for a business user?

Currently running Ubuntu 10.04 and have 3 new Seagate 1TB drives ready for action. Usage includes; open office documents, project management applications, Photoshop files and other desktop applications for business use.

Plan to use Linux software raid vs controller card. Am leaning toward Raid 1 with mirror to a 3rd drive for extra security. My concern with Raid 1 is a possible decrease in speed which, if it occurred would make Raid 1 untenable in my current system (1.6 GHz dual core).

Raid 5 seems like a good alternative, as it may even speed things up a bit, but, is vulnerable to complete data loss if the 2nd drives go down before replacing the failed devise.

Your comments are appreciated.

Thank-you


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a c 289 G Storage
November 10, 2011 7:56:56 PM

You are correct; it is a religious issue.

If you are not buying a separate RAID hardware card, RAID1 simply mirrors the data while RAID5 will use your CPU for parity calculations. Technically, RAID1 would be better for you because it won't tax your CPU with said calculations. That said, CPUs these days are awfully fast and might not notice the load.

RAID1 of three drives is perfectly possible; you stay alive if any two of the three die. But you only get the storage capacity of one drive. RAID6 with four drives lets you support the loss of any two drives and gives you the storage capacity of two drives. But that's just capacity and redundancy issues. 5 and 6 will write more slowly than 1.

FireWire2? Other folks with more real-world RAID experience?
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a c 114 G Storage
November 10, 2011 8:24:45 PM

I store office documents on an NAS in X-RAID.... I couldn't imagine going ay other way at this point for ease of use.
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November 10, 2011 8:46:56 PM

I am just quoting directly off of the other thread because I feel the information is pertinent to the discussion here (and to go along with WyomingKnott):

Branden said:
in my experience, the performance of a raid 5 array is dependant on the controller.

if you're building a raid 5 with your motherboards built-in controller then don't expect much and don't be surprised if you see worse performance compared to a single hdd.
i've got a hardware accelerated raid controller running raid 5, it's out-performs any single mechanical hdd i've had.

EDIT: i have three hitachi deskstar 7k3000 2TB drives in raid 5.
one fo those drives by itself will hit ~115MB/s, but three of them in raid 5 configuration on a hardware accelerated controller card i hit 205MB/s


l0ckd0wn said:
QFT (quoted for truth)

Everything Branden said is pretty spot on.

To give an idea, we use all 3Ware controller cards with 128MB of CACHE on the physical card. When using an onboard solution (Intel RAID, SIIG RAID, etc.) you are not using a dedicated controller to handle the way the data is dispersed, you are using the processor to do a low level "software RAID" which in turn is very time consuming to build the entire array, and the more drives/total storage you have, the longer it takes. For instance my boss built an i5 650 (3.2) on an Intel Extreme MOBO that supports RAID 5; building the actual array while trying to use the computer (Win7 Pro 64bit) took nearly 48hours to complete. A similar setup (Xeon 3.0) with a dedicated controller (3Ware on PCI-X not PCI Express) with same size drives (1.5 TB) took roughly 8 hours to complete from start to finish, and this while the server was under partial load.

The difference is that you have a co-processor specifically in place to handle how the data is applied to the drives and does not rely on the CPU to process the requests.

In my experience (I use HighPoint Rocket RAID as I posted HERE) 3Ware, LSI & Adaptec are pretty much slam dunks for business-grade RAID. As for home applications like I listed, HighPoint seems to do the trick just fine, but I do not use the drive to boot off of and only use it as a storage container.

If you are going to use an onboard solution, I would generally stick to a RAID 1/0+1 and stay away from 5 because the parity sets is the part that takes such a long time to create. Remember that a good setup for super-fast booting and data load is running RAID 0 on 2x SSD drives; lightning fast reads.

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a b G Storage
November 10, 2011 9:26:53 PM

RAID 1 (mirroring) is full duplication of your data, it does not do anything that would speed up things.
RAID 0 will speed up things because basically it stores half of your data on one drive and half on the other, but it does nothing for safety, or it actually makes your data more vulnerable to loss. If either drive fails you lose your data.
RAID 5 sort of combines these 2 things. Using 3 drives for instance it can put half of your data on one drive, the other half on the second drive so that lets it read/write faster, and then it uses the third drive for redundancy. If you lose any of the 3 drives you can still recover your data.

With the sizes of drives available now, assuming you are buying new drives, it is easiest to just buy 2 drives each equal to the amount of data that you want to store, and do RAID 1. If you already have 3 drives and one of them is not big enough, then RAID 5 would benefit you. If you really need faster read/write than you can get with a single drive then go with RAID 0 or 5. If you need more storage than you can get with the biggest drive you have or can buy, then RAID 5 will provide some benefits.
There is another RAID called 1+0, sometimes just called 10, that uses 4 drives and combines them to give the benefits of RAID 1 and RAID 0 at the same time.
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a b G Storage
November 17, 2011 8:15:13 PM

Thank you! WyomingKnot. Sorry I'm quite busy these days... hardly check back here...

Working on several Unified Storage Servers with Dual FC 10Gb systems :-)

For business uses highly, highly recommend hardware raid - hardware RAID has much higher transfer rate in random mode, and requires much less CPU time.

I would rather have 5x 1TB HDD than 3x 2TB HDD because the more spindle the faster it gets.

If you want more reliable, then set a RAID5+hot spare then if a drive failed the spare hdd will jump right in.

This will give you more time to fix the problem and redundancy
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