Re: Raid 0+1

[Sebastian Riemer <sebastian.riemer@profitbricks.com>]

On 30.11.2012 15:27, Sebastian Riemer wrote:
> On 30.11.2012 14:25, Oguz Yilmaz wrote:
>> What is the suggested way for making Raid 0+1 (not 1+0)?
>> Is it possible to make it without LVM?
> 
> Yes, it is possible but it only makes sense if you want to mirror to
> another server as most people know that the alternative DRBD is too slow
> for serious storage requirements.
> 
> Create the RAID-0 first, then take your RAID-0 device and e.g. an iSCSI
> device from another storage server with the same setup and create a
> RAID-1 over them. Then, you've got your stacked MD layers.
> 
> With the flag write-mostly you can even tell the read balancing that the
> remote device is slower than the local one.
> 

I've forgotten to mention: You need a kernel >= 3.4.2 for this.

Earlier kernels don't support bvec merging and therefore every IO is a
slow 4 KiB IO in that RAID 0+1 setup.

Btw.: LVM also supports striping but letting LVM do striping is only
useful if you want to build RAID 1+0. The speed is the same as "RAID 1+0
+ LVM". Only that raid10 driver doesn't scale good for >= 24 HDDs.