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On Wednesday 16 June 2010 04:43:06 martin f krafft wrote:
> also sprach Boyd Stephen Smith Jr. <bss@iguanasuicide.net> [2010.06.15.2108 
> > > Use mdadm for a RAID5 or RAID6 and LVM on top for the remaining
> > > cases when you need space and care less about performance.
> > 
> > Use RAID 1/0 in mdadm when you need redundancy, space, and performance.
> > 
> > (Although, IME, RAID 5 is not badly performing.)
> Sure it is, on writes. If you have the right hardware, you won't
> notice, but every write takes twice as much work.

But not twice as much time, which is what performance is about.  When you are 
writing to two disks in parallel, that has (roughly) the same performance as 
writing to a single disk and (roughly) twice the performance as writing to two 
disk serially.

I've used RAID 5 for years, both HW RAID and SW RAID.  I have never had issues 
with write speeds.

> > RAID 1/0 through mdadm with 4 disks is also better than strictly layering
> > the RAID levels.
> Do you have any data to back this up? Fundamentally, the data will
> traverse one layer less, but does it actually make a difference?

It uses a different layout which spreads reads and writes more evenly across 
the drives.  This results in higher performance on the same number of disk 
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