another raid question... identical drives or not?

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Ok so i read a rule of RAID is that you should use identical drives... yet it seems that not everyone follows this rule.

I just bought a 3ware amcc 9650se-12ml (12port) raid controller to build a RAID 6 array. The data im trying to protect is VERY important to me, ie ~3TB of university phd data, so i need to get this right (and YES i am still backing up !).

I already have 2*seagate barracuda 500GB 7200.10 drives, and 3*western digital 500GB wd5000ks drives. However, these drives are full of data. So no matter what i need to buy at least 4 new drives so i can build the raid 6 array.

How critical is it that drives are of identical type (bearing in mind how badly it would screw my life over if i lost this data). So if i need to keep the drives of identical type, then are the wd5000ks drives completely different from the wd5000aaks drives that OcUK are now selling? (ie is it a bit like 7200.10 and 7200.11 drives?). Or is it ok to mix wd5000ks and wd5000aaks drives? Is it a bad idea to mix the 7200.10 drives with the wd5000ks or wd5000aaks drives?

If i cannot mix the seagates and western digitals, or wd5000ks with wd5000aaks, then what 500GB drives are the best atm?

Thanks ! :)
 
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Generally it's recommended to use identical disks since otherwise you'll end up losing some of the space and performance benefits of the larger and faster disks. But it's certainly quite possible to build arrays with slightly different sets of disks. It doesn't sound like the disks you intend to use are worlds apart so I would suck it and see how it goes.

Note however to build a raid array you'll have to use empty disks - there is in all likelihood no way that you can keep the data on the drives and yet build them into a RAID6 array. You will have to backup the data (and verify the backup) somewhere else, build the array, then restore onto it. (Probably be a good idea to have 2 backups...)

Edit: BTW, you do realise that for 3TiB of data stored on RAID6 array, you'll need a little more space than you're planning for -- you'll ned at least 6x 750GiB disks or 8x 500GiB disks. If you already have 5 disks full of data, then you've got a bit of a problem getting that onto a new array, unless the data is compressible and you can pare it down temporarily onto fewer disks.

See e.g. here: http://dorm.tunkeymicket.com/raidcalc/index.php
 
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Thanks for the help :)

ByteJuggler said:
Note however to build a raid array you'll have to use empty disks

yep dont worry im going to buy 4 new drives to build the raid 6 array. Then i will transfer data off one of my currently full 500GB disks onto the array, then plug that disk into the array, and so on. I just wanted to be sure that buying four wd5000AAKS 500GB disks and then pairing them with 3 wd5000KS was going to be ok.

ByteJuggler said:
Edit: BTW, you do realise that for 3TiB of data stored on RAID6 array, you'll need a little more space than you're planning for

Yep dont worry i got that covered. I dont need 3TB straight away. I will buy 4 new drives and i have 3 existing wd5000ks or 2 existing seagate 7200.10 drives. I only need 2TB at the moment. Oh and a hotspare would be good.


Perhaps i should just buy 4 new 7200.10 500GB drives. Then i will have 6 identical drives. I was being a bit of a cheapskate thinking of building the array with the western digital drives simply because i have one more of those.
 
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