Study Notes

I used two IDE harddisks(one is ST 40G’/dev/hdb’,and the other is WD 120G’/dev/hdc’) to build soft RAID 0 on Linux.As I read from book,RAID 0 is a striping array which data will be written to the disks in sequence,that’s also what call it “stripe”. This array should be idenfied by the smallest disks capacity for spreading data in stripe mode. So, I think the capacity of RAID0 is equal to twice of smallest one. In the way, my soft RAID0 should be 80G(2x40G)

The following lines are issued to create RAID0:
# mdadm -C /dev/md0 –level 0 -n /dev/hdb /dev/hdc
# cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 hdb[0] hdc[1]
159142336 blocks 64k chunks

I found the capacity of my soft raid 0 is 160G.It made me confused,how does RAID0 work as the end of writing over 40G in each disk?

The size of a RAID0 array is equal to the sum of the sizes of the individual volumes. The way the stripes works is that the first 80gigs will be striped between the two drives–resulting in roughly twice the read/write speed of the slower drive. The remaining 80gigs will be on the larger drive only–it will be only as fast as the larger drive.

You don’t really have any control over whether certain files are in the “fast” half or the “slow” half. If you’re particularly concerned about performance, it may make more sense to split the larger drive into multiple partitions–one 40gig partition to RAID0 with the other drive, and one 80gig partition to be “slow” storage.