Archived from groups: alt.comp.hardware.pc-homebuilt (
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pascaljr@gmail.com wrote:
> I have two 120 GB hard disks set up on a RAID 0 setup,
I'm not so sure about that.
> and I have a
> question. The main objetive of using a RAID 0 setup is for performance,
> since half of my data will be stored on one disk and the other half is
> stored on the other disk, right?
Close enough, in a broad brush sort of way, although a bit short on the
particulars.
RAID 0 does not place 'whole files' on one or the other of the two disks so
that the file sizes add up to half and half. Files are broken into stripes
of a size dictated by the user-defined "stripe size" of the array, and
stripes are sent to each disk in the array.
For example, say you have three files of 'size' 10 (file 1), 10 (file 2),
and 20 (file 3). RAID 0 does not put the two 'size 10' files on one disk
and the 'size 20' on the other so that "half of my data will be stored on
one disk and the other half is stored on the other disk."
Rather, each file is broken into the "stripe size," let's say that's 2. So
the first 2 of file 1 goes to disk 1, the second 2 goes to disk 2, the
third 2 goes back on disk 1, the fourth 2 goes on disk 2, and the fifth 2
goes back on drive 1. And the same process takes place for file 2 and file
3 so that 'half' the data of *each file* is on each drive.
> Now, when I defrag, it seems like all
> the data is shifted to one of the disks, leaving the other one empty,
Which makes no sense at all because RAID 0 handles the data/drive split and
a RAID 0 array will appear as one drive to the system, and to defrag, and
to you. So there's no way defrag can move the data to 'one of the disks',
or alter the data split in the array, nor would you be able to tell even if
it did.
Look up above at how RAID 0 works. It is not possible to say that a file,
much less all of them, is on 'one disk'. As long as it's larger than the
stripe size it MUST be on both disks, or it isn't a RAID array.
Which leads me to believe you don't have them setup as RAID 0, even though
you may think so, and I suspect you simply put them on the RAID controller
but did not define a RAID array.
> which pratictly blows the whole RAID 0 objective. Am I wrong? If I'm
> right, is there a defrag tool that would split up the data correctly?
Well, not being 'wrong' on one matter doesn't mean your conclusion derived
from it is necessarily right because you're missing a few more bits to the
'how it works' part. Yes, it puts half on each (with a two drive RAID 0
array) but, no, there is no defrag tool that will split it 'correctly'
because it doesn't know a thing about the split, or that there is even more
than one drive. That's all done by the RAID array.
> Thanks,
> Pascal
>
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