RAID Question...

[bob4432]

within the past 2 mos i ordered a 500GB maxtor hdd, and now i see in the hot deals that there is a wd 500GB on sale. with the price of these drives and the available hardware i have, some type of a nas box may be in the works, in a raid 5 or 6 array. so with a array like 5 or 6 is it best to have all of the same bramd / model # hdds in the array or does it really matter?

the reason for the question is that i like to try out different hardware, but i don't want to waste $$ when the it comes time to build the nas box, and i am in need of another 500GB hdd....

performance is not an issue as my main rig runs 15k hdds, so the difference in performance that a 7.2k hdd offers doesn't mean anything to me as it will just be a backup setup.

 

[Beatnik]

Uh, yeah. Just think about it for a second. You have a "stripe", and 2 words are data and 1 word is parity... basically that's a tuple. So... You can use different sizes, but in a lot of cases that will reduce you to using the smallest drive as the determiner of all useful drive size. So for example, if you had a 250GB drive, anything over 250GB on the other drives would be a waste.

... all that being said, some of the tricky onboard raid software can do multiple volumes of different types involving a single disk. But usually people don't really want to do things like that.

 

[bob4432]

the hdds will all be the same size (give or take a few MBs depending on how the hdd formats), just possibly different brands, or is it best to run 1 brand/model of hdd?

 

[Beatnik]

It is better to run similar performing drives. So if it is easy to get same drives, that's fine. Same logic. The worst performing drive is going to control the overall behavior of the RAID5.

At the very least I would make them all the same RPM speed... i.e. 7200 or what have you.

 

[dakels]

beatnik is right. While it doesn't matter what brand, model, or even size of the mix of drives, the RAID will function to the weakest link. Will this be a hardware RAID I assume? Onboard controller? Some RAID cards can be a bit finicky but most nowadays won't care what drive you have in there as long as the stripe partitions are the same size. Shouldn't cause any issues down the road for different brand/model drives of similar specs.

 

[bob4432]

it will be probably one of the hardware 8port sas/sata raid 5/6 controllers in a 1-4x pci-e slot or even in a 32bit pci slot - whichever is cheaper in that regard as i won't need much bandwidth - 50MB/s str would be more than enough and with a larger card adding additonal hdds is the key. will probably wait a bit for the controllers to come down in price, but figured since i was buying drives and will use them now, may as well get stuff that is compatible for a future venture

thanks all for the input

 

[dakels]

The main factor IMO for you to choose a higher end RAID card over an on board system that could handle it is what you plan on using this NAS for. If this server will be handling alot of concurrent I/O requests then you will want to beef up the bus and RAID card. If this is more for small audience or personal, then all you really need to worry about is transfer rates and data security. A few motherboards do have RAID 5 capability plus 8 SATA slots but an independant PCI card would be better of course for its individual subsystems which help take a burdeon off the mainboard and speed things up in many cases. A high end card with a IO subprocessor and independant cache RAM can speed up potential performance a lot. Remember though, with most striped RAID systems, if the controller gets hosed, you often need an identical controller to restore your data quickly though there are some ways around this.

If it were me and I was investing in a 8 drive NAS, then I would get all identical drives unless say I had 4 drives already or something. When dealing with that many, limiting your diversity often narrows your troubleshooting when there is a problem. It all depends on your situation and your needs.

 

[Madwand1]

Every vendor would tell you that it's generally best to have all identical drives, but that it's not a hard requirement. Think about it -- HDs change far too frequently to be able to guarantee an identical replacement. Maxtor HDs of one year ago are no longer available. In the lifetime of your RAID array, odds are very high that the drives that you started off with will not be available when it's time to replace or upgrade capacity, and who knows what Maxtor drives if any will be available in this class down the road. But that's fine, as you can mix and match.