Linux software RAID: How to use drives of unequal capacity

ech1965

New Member
Apr 3, 2011
2
0
1
Hello,

I'm rebuilding my home server ( mainboard GA-M85M-US2H, athlon x2 245) based on ubuntu server.

I can assign 5 drives to the server:

2x 1To
1x 1.5 To
1x2To
1x 500Go

I'm trying to find the best layout based on mdadm raid: ( Please no LVM at this time)

Basically
- Raid 5
- minimal wasted space,
- minimal number of mountpoints

My current plan is

1 To |________|
1 To |________|
1.5 To |________|____|
2To |________|____|____|
0.5To |____|

-> md0 : Raid5 4x 1To-> 3To net
-> md1 : Raid5 3x 0.5 -> 1To net
-> 500gb without redundancy

I was wondering: Would it be possible to build a Raid 5 on top of a JBOD ? to get this layout

|________|________| 2 x 1to
|____________|____| 1.5 + 0.5
|_________________| 2 tO

-> I'd have 6to brut-> 4To in raid5 with one joker ( 1 drive can fail without loosing data)

Thanks for reading and commenting ...
Etienne
 

john4200

New Member
Jan 1, 2011
152
0
0
Why do you use "o" instead of "B" for bytes? It makes your post hard to read.

Your first example should work.

Your second example is not feasible, as far as I know. How would you possibly create the "JBOD" of a 2TB disk from multiple disks in such a way that mdadm could use them?
 

ech1965

New Member
Apr 3, 2011
2
0
1
Why do you use "o" instead of "B" for bytes? It makes your post hard to read.

Your first example should work.

Your second example is not feasible, as far as I know. How would you possibly create the "JBOD" of a 2TB disk from multiple disks in such a way that mdadm could use them?
Thans for your answer.
O because My mother tonge is french and some of us use the word octet instead of bytes!
Regards,
Etienne
 

TuxDude

Well-Known Member
Sep 17, 2011
615
338
63
Why do you use "o" instead of "B" for bytes? It makes your post hard to read.

Your first example should work.

Your second example is not feasible, as far as I know. How would you possibly create the "JBOD" of a 2TB disk from multiple disks in such a way that mdadm could use them?
The second method should work too. You build the 2TB sub-arrays using mdadm in linear mode, then create the raid-5 using those devices. It's basically the same thing as RAID-10 layering raid-0 over raid-1, except this is using raid-5 over linear (for some members).