Re: RAID 6 mdadm

[Gary Dale <garydale@rogers.com>]

On 10/04/13 12:05 PM, Ross Boylan wrote:
> On Wed, 2013-04-10 at 17:57 +0200, Dexter Filmore wrote:
> > Am Wednesday 10 April 2013 17:21:35 schrieb Muhammad Yousuf Khan:
> > > exactly, i am using RAID 1 with mdadm and not more then 230 or 300MB
> > > throughput.  and the people are harnessing 4GB so this is the point
> > where i
> > > am confused
> > You cannot get more than about 200MB/s out of a RAID1 setup, not even
> > with
> > 15krpm SAS drives. the RAID1 will never be faster than a single disk.
> > How
> > would it.
> It can read faster than a single disk by combining reads from different
> sectors on different disks.  I think your assertion is incorrect for
> reading, though  not for writing.
>
> Ross Boylan
Exactly. Most data is read more often than it is written so that read 
performance is critical.

In the particular setup of RAID6 with only 3 drives, each drive gets the 
same amount of information as they would in RAID1 so that write 
performance also does not change. However RAID1 requires less CPU time 
and is arguably more reliable (please let's not start a debate on this - 
it's not a big issue).

The advantage of RAID6 comes when you have 4 or more disks. Because each 
disk then gets only part of the data, write performance can improve.