[Discuss] btrfs

[dsr at randomstring.org (Dan Ritter)]

On Mon, Feb 25, 2013 at 10:53:28AM -0500, Derek Atkins wrote:
> Dan Ritter <dsr at randomstring.org> writes:
> 
> >>   mkfs.btrfs -d raid1 /dev/sda /dev/sdb /dev/sdc /dev/sdd
> >> 
> >> It this going to be more like raid10?
> >
> > No, that's still RAID1: two copies of every file, no striping.
> > If you want striping+mirroring, turn on -d RAID10. 
> 
> How is it still raid1?  Maybe my definitions and your definitions are
> different here.  Let's say that each device is 1TB.  If I have 2, then
> obiously I only have 1TB of storage because each extent is duplicated on
> both drives.  However if I have 4 drives, you imply I get 2TB of storage
> (because still, each extent is mirrored on two drives).  But what I
> don't understand is how is this not effectively "raid 10"?  You're
> combining storage from multiple drives into a single filesystem larger
> than the mirrored drives.


linear is concatenation: after you fill the first disk, fill the
second... 

raid 0 is striping: split the data and write parts to all disks
at once. 

the n>2 raid1 is essentially mirror + linear.

raid10 is mirror + striping.

-dsr-