RAID 5 data structures

[Sam Leon]

I have a funny question.  I have been playing with a 3 disk raid 5 setup 
for my desktop.  I guess I don't fully understand how the "stripe" is 
managed or even what it is.  I know the stripe is made up of a chunk 
from each disk.  Now I always thought of the stripe in raid the same as 
a block in ext3 or a cluster in ntfs.  Meaning if I have a 1k file that 
I write to an ext3 filesystem with 4k blocks, my 1 k file will take up 
one block thus wasting 3k of space.

Now I thought the stripe in raid followed the same principle.  Meaning 
if I have a 3 disk array with 64k chunks then my data stripe is the 
number of disks minus one drive because of parity so in this 3 disk 
array I would have a data stripe of 128k.  So how much of that space 
would my 1k file take up?  Would it take up the whole 128k stripe or 
just one chunk leaving the other chunk free for something else?

When I migrated my root drive over to the raid5 array I made, I was 
afraid that it would use alot more space on the raid array since it is 
full of very small files but to my surprise df -h reported the same 
values for / on the array and / on the single disk that I had copied the 
data from.  So what is going on here?

Thanks,
Sam


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