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I want to setup a dedicated server. To begin with we need a minimum of 8TB. I believe I can begin with 6x2TB drives in a RAID6 setup to achieve this.

Now when I need to increase this capacity to 10TB. I should be able to add a single 2TB disk to the array.

But is it as simple as just adding another disk. Will I lose any data from my existing drives?

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2 Answers

Your math works out, but take into account that a 2TB drive doesn't deliver 2TB raw, it will be 1.8 or 1.7 so you may need 7 x 2TB drives to get that 8TB usable number.

That being said, a good controller should be able to expand the logical unit to include the new drives, but you'll have to look at the capabilities of the controller. Also keep in mind that your partition inside that logical unit won't expand automatically, you may have to do this after the fact. I'd suggest some kind of logical volume manager like LVM, EVMS, or if this is Windows perhaps set it as a dynamic disk.

Test, test, test, and more testing.

Tom

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The part of this answer regarding partitions is vital. Many hardware based controllers support expanding a raid array but people tend to forget about the need to then expand the partition on the volume. The partition knows nothing about the raid array and vice versa. –  ManiacZX Nov 3 '10 at 19:43
    
No joke, I've seen too many people get burned by this. Whatever partitional or LVM scheme you end up with please TEST expansion and the procedure to do so before putting into production. You don't want to guess at this AFTER the fact. –  SpacemanSpiff Nov 3 '10 at 19:48
    
If we are talking about "marketing Bytes" and "IT Bytes" it's best to use the ISO prefixes to avoid ambiguity: 1TB = 1000000000000 Bytes, 1TiB = 1024^4 Bytes = 1099511627776 Bytes –  Hubert Kario Nov 3 '10 at 22:43
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Well you don't mention how you're going to build this R6 array (i.e. via hardware controller? if so which one, of if by software then which OS/version) - but generally you can add extra disks to R6 arrays but I couldn't confirm without these details.

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I have just been told by my provider that RAID6 is not an option. only RAID 0,1,5,10 are available which is not ideal. We have 8TB worth of data currently so RAID10 is too expensive...and 5 I would prefer to avoid. –  Paul Hinett Nov 3 '10 at 19:37
    
Well RAID5 will let you get to your 8TB with just the 6 drives, and you can leave some hot spares. Are you THAT concerned about dual disk failure? –  SpacemanSpiff Nov 3 '10 at 19:47
    
well im worried about losing all my data due to disk failure...i run a busy media website, if i was to lose the data it would be devestating. I am thinking of using an alternative data backup solution...probably a seperate dedicated server. I think i need to repost this as a seperate question though. –  Paul Hinett Nov 3 '10 at 19:54
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It's not dual disk failure that worries me about R5, it's missed single-bit errors (google why people hate R5, there's lots about). Paul if your data and service is valuable to you then you really need to take this seriously, stop using consumer/prosumer SATA drives and do the job properly - otherwise it's only a matter of time until you'll be sat there with no website until you've restored 10TB from backup, which will be slow no matter what it's from. –  Chopper3 Nov 3 '10 at 20:02
    
I agree with Chopper. Perhaps a dedicated device for storage is in order here? Replicated to another similar device? –  SpacemanSpiff Nov 3 '10 at 20:54
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