RAID5 Setup

[aye29]

I'm considering setting up a RAID 5 array with 4 WD 250Gb hard drives. How much hard drive capacity will I lose from using a RAID 5 array as opposed to not using RAID? Also how similar do the drives in the array have to be? I'm pretty sure they have to be of the same capacity but do they have to be same manufactuer, model and specs as well?

 

[InlineFour]

total HDD - 1. so you'd have 250gb x 3 = 750gb.

always use the same capacity hdds for all your hdds.

it's always best to use identical hdds for your raid, however, it's not mandatory.

 

[Kartajan]

RAID 5 likes the drives to be as similar as possible, you get the lowest common denominator of all of the drives in the array

(If one is an 80 and the rest are 120's, it seems like they all are 80's, etc..)

For RAID 5 the array uses one drive for parity, and the rest are a big "virtual" drive.

if you have 4 250's, then you will have a 750G array. More drives up to the limit of your controller is better. Note that any speed benefit is lost if you do not have a RAID conroller that does the math onboard. (True Hardware RAID)

The fun thing is that you really should get one extra drive to hang on to in the rare event that a drive fails, as you would not be able to use the system until to rebuild the array..

 

[aye29]

Does the hit to array performance when using software RAID 5 only effect writes or reads or both? If I did create a RAID 5 array I'd probably be using the Silicon Image Sil 3114 chip on my motherboard. Since I already have my OS installed on a Raptor, I'm planning on using the array as a media storage system so I'm more concerned about read speed that I am about write speed.

 

[obeseotron]

For redundant media storage, software raid5 should be fine. Write speeds will be much lower than even a single drive, but read speeds should be comparable to a single drive. CPU usage is not good, especially on writes. Check gamepc.com for specific numbers.

I wouldn't want to tie that much data to the motherboard though, you can get get cheap pci cards with the same chip on it for less than $30. Moving arrays from one motherboard to another is dicey at best, and this way you won't have to worry.

 

[aye29]

Where can I get a PCI SATA Raid 5 card for cheap? All of the cards that I've seen on Newegg cost 250+. They are probably true hardware Raid cards which I dont need for my purposes.

 

[piasabird]

Dont trust a Raid Array unless you have a tape backup unit.

Another think is you need air flow around the drives, and a case with good ventillation.

 

[BDawg]

Originally posted by: Kartajan
For RAID 5 the array uses one drive for parity, and the rest are a big "virtual" drive.

Isn't it RAID 3 that uses one drive as parity? RAID 5 assigns the parity to different disks.

Don't forget to put in a hot spare.

 

[Fullmetal Chocobo]

Originally posted by: BDawg

Originally posted by: Kartajan
For RAID 5 the array uses one drive for parity, and the rest are a big "virtual" drive.

Isn't it RAID 3 that uses one drive as parity? RAID 5 assigns the parity to different disks.

Don't forget to put in a hot spare.

Yes, you are correct. But I think he was speaking in reference to space available in a RAID 5 configuration.

 

[obeseotron]

Originally posted by: aye29
Where can I get a PCI SATA Raid 5 card for cheap? All of the cards that I've seen on Newegg cost 250+. They are probably true hardware Raid cards which I dont need for my purposes.

You're right those are hardware cards. You can get cheap PCI cards with a Sil3114 for as little as $20 before shipping. That's the same chip as your motherboard, drivers should provide raid5, no worrying about migrating to a new system as long as it has a pci slot.