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Assume that I built an 2TB RAID5 array and its running and some data is stored on it.
Now I need to increase its size to 5TB.
Can I increase capacity (By adding extra drives)? How?
If Yes is it possible to do this while RAID array is working?
I'm going to use Linux as OS.
I don't mind any special controller; I just want to know is it possible or not;

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closed as not a real question by Wesley, Ward, Scott Pack, Shane Madden, MadHatter Oct 6 '11 at 14:27

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

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This depends completely on what's handing the array. Is it a hardware RAID controller? If yes, what model? If no, what OS is the software RAID running on? –  Shane Madden Oct 5 '11 at 21:09
    
@Shane Madden. I don't mind any special controller; I just want to know is it possible or not; and if yes what features controller must have? and about OS, I want to use LINUX (Maybe Ubuntu) –  4r1y4n Oct 5 '11 at 21:13
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2 Answers

Linux MD software RAID can add disks to a hot RAID-5 array (mdadm --grow), reshaping the data on the fly. Don't proceed until the reshape finishes (cat /proc/mdstat).

You'd then need to expand your filesystem to fill the array. For an ext2/3/4 filesystem, for instance, you'd then run resize2fs to expand your filesystem to use the newly available space on the device.

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«likely need a full, offline fsck» — BS. –  poige Oct 5 '11 at 21:47
    
@poige Right you are. Edited. –  Shane Madden Oct 5 '11 at 22:31
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Answer depends on what exactly RAID-5 implementation you'd use. Linux Soft RAID (LSR) allows for both on-line adding drives into RAID-5 (re-shape) and replacing drives with bigger ones then increasing overall size. I think some RAID-5 controllers should have supported this too, but don't expect them to be cheap. Lots of Linux filesystems allows for online size grow, but not shrink usually.

In case you go with either RAID it makes sense using LVM-2 too. You can merge several RAID-5 arrays into single logical volume with it, for e. g..

P. S. RAID-5 may be not optimal solution — just think: either disk you lose and your array is performing sub-optimal × not having redundancy.

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