Anyone have a Drobo? Super confused about volume size and thin provisioning.

fuzzybabybunny

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I just got the Drobo Mini and since it only supports 2.5" drives I've installed four 1TB disks in it. I don't foresee 2.5" disks to expand much past 1.5TB for a long time.

Four 1TB disks = 4TB, but since it uses RAID I figure that I should have 3TB actually available to me.

During setup it asked me what I want the Max Capacity / Volume Size of the Drobo to be. It said that Max Capacity is the maximum that I ever plan on having the Drobo be. So I selected 16 TB, even though the drive actually only has 4TB and 2.6 TB available.

Windows shows the drive as being a full 16TB. What happens when it reaches 2.6TB? It'll show the 16TB as not being full, but the actual disks will be full. And when that time comes 2.5" disks will still be around 1 TB.

I'm just confused on what I should expect when this happens.
 

vshah

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Sep 20, 2003
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it will notify you that your usage is approaching physical disk limits, and it will ask you to add new drives or replace with larger drives (one at a time, with time to rebuild in between) in order to meet the growing storage need.
 

fuzzybabybunny

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it will notify you that your usage is approaching physical disk limits, and it will ask you to add new drives or replace with larger drives (one at a time, with time to rebuild in between) in order to meet the growing storage need.

So once that limit is reached, and I put, say, one 2TB drive in there, so I'll have three 1TB and one 2TB, there will be no data loss and I'll have 1TB more?


Also, just for future reference, 2TB 15mm 2.5" drives have been available for a while and Seagate has also launched one in 9mm that is available in very small quantities (wil ramp up eventually). :)

http://www.seagate.com/about/newsro...ivision-ships-2tb-storage-solution-pr-master/

Damn. The drobo doesn't support 15mm drives :(
 

Mark R

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Oct 9, 1999
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So once that limit is reached, and I put, say, one 2TB drive in there, so I'll have three 1TB and one 2TB, there will be no data loss and I'll have 1TB more?

Pretty much. But it's a bit more complicated than just that.

Let's say you have 4 1TB drives with single drive redundancy, giving 3 TB of capacity.
To upgrade capacity, you swap 1 drive for a 2 TB.
No data will be lost, and the system will rebuild, but you still only have 3 TB of capacity.
Once rebuild completes, you swap a 2nd drive for 2TB.
Allow the system to rebuild again. You now have 4TB of available capacity.
Swap 3rd drive.
Still 4 TB available.
Swap 4 th drive, now you have 6 TB available.

As long as you allow the system to finish rebuilding (about 12 hours) between each drive swap, no data will be lost. However, note that during a rebuild, there is no protection from drive failure. If a drive dies during a rebuild (and a rebuild really thrashes the drives), the whole array is toast.
 

fuzzybabybunny

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To upgrade capacity, you swap 1 drive for a 2 TB.
No data will be lost, and the system will rebuild, but you still only have 3 TB of capacity.

Why won't the capacity increase a little bit if I replace a 1TB drive with a 2TB drive? If the capacity doesn't increase, what's the point of replacing a drive with one of higher capacity?
 

vshah

Lifer
Sep 20, 2003
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raid 5 and similar schemes are limited by the size of the smallest drive in the data/parity array.
 

Mark R

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Oct 9, 1999
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Why won't the capacity increase a little bit if I replace a 1TB drive with a 2TB drive? If the capacity doesn't increase, what's the point of replacing a drive with one of higher capacity?

No. When you upgrade just 1 drive, you add a whole bunch of new capacity, which is not matched by any other drive.

There is no way to apply data protection to that extra bit as there is no spare capacity elsewhere to utilise to store the parity.

The drobo's proprietary parity system is better than RAID. Unlike RAID5, upgrading 2 drives WILL give you extra usable capacity, whereas with a traditional RAID, ALL drives have to be upgraded before the extra capacity becomes usable.