Can I change HDD brand in a raid array?

Right now i have a RAID 5 Array with 4 3TB Western Digital WD Green WD30EZRX. I've read reviews on HDDs for RAID and i saw that Hitachi ULTRASTAR are one of the best for RAID. I would like to move to the Hitachi HDDs but my server is live and has lots of data on it. So my question is can i swap out my WD HDDs one at time until they've all been replaced? or do i have to take the hit and redo the array from scratch?
ronfastI.T. DirectorAsked:
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Bill HerdeOwnerCommented:
You can swap them one at a time allowing the rebuild to complete each time before proceeding to the next.  It is risky, and good backups are a bit important.  If you have other storage to keep the data on, the rebuild from scratch may take less time.

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Chad FranksSenior System EngineerCommented:
You can swap out one of the disks in the array and let it rebuild. Once that is complete repeat the process until all the HDD have been replaced.  If you do this in the middle of the day make sure you lower your rebuild rate or the disk will get too much IO and cause performance issues.
ronfastI.T. DirectorAuthor Commented:
I split the points between the two of you because you both had different, good info.
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ronfastI.T. DirectorAuthor Commented:
One more question. . . should i avoid refurbished HDDs? they are half the price
rindiCommented:
You should always only use those disks that are sold by your server manufacturer for your particular RAID controller, they use adapted firmware and work best with that server. If you can't go for those, then at least use enterprise class disks. Your WD green are absolutely not built for use in servers, they are mere consumer grade disks for use as single disks in PC's. Never use those in servers!

I would also never use RAID 5 these days. That is old stuff and unreliable compared to other RAID arrays like RAID 6, 1 or 10. It is also more difficult to properly manage and you can cause a lot of damage through wrong manipulation or human error. Besides that, a rebuild on a RAID 5 array, particularly if you are using very large capacity disks like you are using now, will take very long, and during that time your complete array is in the highest danger of total data loss. RAID 5 may have been OK a decade or longer ago when your disks had a very low capacity and were very expensive, and you had to maximize the capacity to as low a number of disks as possible. But with today's huge disks that is no longer a problem.

In your case your only sane option is backup, remove your disks, get the officially supported disks from the server manufacturer and replace them, build a new RAID array, preferably RAID 6, then restore from your backup. First that will be much faster, and in your case as you are using SD Green disks currently, you'll almost certainly have 100% data loss if you wait for your array to rebuild after replacing each disk.
ronfastI.T. DirectorAuthor Commented:
Okay, great input. My server is a glorified Desktop that i put together, with a Xeon X3450 proc, 24GB RAM. It has a Dell PERC 710P controller with 2 channels. i have 2 volumes, 1 for the system (mirrored) and 1 for the data (raid5) so that leaves me with 4 HDDs for data so I wouldn't be able to go to  Raid 6. So i'm stuck with RAID 5. The data can be replaced because it's a back end server, it just would take a while so I could build it from scratch. I'd love to go to RAID 6.

So it looks like HHD4K Dell 3TB 6G 7.2K 3.5 SATA HDD w/F238F would be the drives i should get since i have a DELL PERC controller
ronfastI.T. DirectorAuthor Commented:
Oh i just checked the specs and i can have 8 drives total it looks like
jmcgOwnerCommented:
How are you set for drive bays in your chassis? You can get adapters that allow you to double up 2.5in drives in 3.5in bays, but you may have to shop around for the right power adapters and check that you have the right cables for the PERC to be able to plug in all the drives you want to use.
Bill HerdeOwnerCommented:
You won't get much performance out of 2.5 drives unless you are springing for SSD. My bench system does use them for the system disk as a mirrored pair, but the work is done on the raid.  I agree with above comments that raid 6 is preferred as you start running larger disks. I have 8 each 2TB drives on a rocketraid (cheap!) controller.  Rebuild can take more than a day unless you bump the priority.
ronfastI.T. DirectorAuthor Commented:
Thanks for your continued comments. SSDs this large are cost prohibitive. I love the DELL PERC since it has 1GB Cache. It increased the disk R/W by at least 2 fold if not more.I have, Samsung EVO 840, SSDs as the System drive (mirrored). I'm going to attempt to connect more HDDs so i can move to RAID 6. So Billheerde, you must have cables that are 1 to 6 then? i'm still confused about teh cableing. i think when i checked i could only find 1 to 4 Sata connectors so i had assumed that i could only have 4 HDDs connected.

once again thank you all for educating me. It's most appreciated.
Bill HerdeOwnerCommented:
No, the controller has two plugs for the raid so I have 1 to 4 connections.  The boot drives just use the motherboard connections and mirror with windows.
ronfastI.T. DirectorAuthor Commented:
Got it. . . . finally.
andyalderSaggar maker's framemakerCommented:
>You won't get much performance out of 2.5 drives unless you are springing for SSD.

That's not correct, 2.5" 15K enterprise disks are faster seeking than 3.5" 15K ones.

Regarding the H710 controller it can actually support 32 disks although you would need a backplane with a SAS expander since, as you've noted, it only has two 4-lane SAS connectors on it so 8 disks if you use fan-out cables.
ronfastI.T. DirectorAuthor Commented:
I finally understand. Looks like i'm on my way to RAID 6 at least.
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