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Today I set up my first RAID ever. I decided to use RAID5, because I want as much space as possible, but I'm to afraid to use RAID0 because of possible data loss.

I have 4 0,5TB drives and in RAID5 I have about 1,36TB usable. That's fine by me.

Now I have a question. I'm thinking about purchasing a 2TB drive and can't figure out if it is possible to add it to this RAID (4*0,5TB + 1*2TB HDD) and how much space will I gain.

I hope someone can answer me, it would help a lot! Thank you in advance.

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up vote 1 down vote accepted

If you use a hardware RAID controller then it depends on the card if it is possible or not. And if you use software RAID on the software.

However many HW cards as well as Linux software will allow you to use the 2TB drive as a fifth ½TB drive, resulting in a RAID 5 configuration with 2TB available space. (5 drives, size of smallest drive, minus one drive for parity).

You might even get away with partitioning the 2TB drive in a ½TB and a 1½TB partition and use the first part for the RAID and the second part as just a simple partition.

But as I wrote before, a lot of that depends on how you set up your RAID.

Also, I keep adding this to RAID posts, but:
1) Please do not replace backups with RAID. RAID is good, but do make backups.
2) Check Serverfaults canonical question about RAID. Specifically the disadvantage of RAID5 and large disks. (Rebuilding if a drive fails is going to take a very long time. And during that time disks will be stressed and much more likely to fail).

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