Re: RAID-10 near vs. RAID-1

[Piergiorgio Sartor <piergiorgio.sartor@nexgo.de>]

On Wed, Jun 12, 2024 at 01:04:18AM +0200, Reindl Harald wrote:
> 
> 
> Am 11.06.24 um 20:31 schrieb Piergiorgio Sartor:
> > I'm setting up a system with 2 SSD M.2 (NVME).
> > 
> > I was wondering if would it be better, performace
> > wise, to have a RAID-10 near layout or a RAID-1.
> > 
> > Looking around I found only one benchmark:
> > 
> > https://strugglers.net/~andy/blog/2019/06/02/exploring-different-linux-raid-10-layouts-with-unbalanced-devices/
> > 
> > Which uses mixed SSD, NVME and SATA.
> > 
> > Does anybody have any suggestions, links, or
> > ideas on the topic?
> > 
> > BTW, practically speaking, what's the difference,
> > between the two RAIDs?
> 
> i wouldn't even consider a RAID10 with two disks, especially with SSD and
> practically you end with a unsupported RAID1 because there are no stripes
> with 2 disks
> 

Hi, thanks for the answer.

I'm a bit confused here. What do you mean
with "unsupported RAID1"?

As far as I know, but please correct me if
I'm wrong, a Linux md RAID-10 *near* layout,
with 2 devices, has identical data distribution
as a RAID-1 with 2 devices.
Meaning the 2 devices are a mirror.

The difference, if I understood it correctly,
is that the RAID-10 has chunks, and hence stripes,
while the RAID-1 does not have stripes.
Furthermore, the read operation on RAID-10 are
interleaved, delivering (for SSDs) double
sequential read speed (for 2 devices), while
the RAID-1 can handle two independent (one per
device) read stream, each with single device
reading speed.

Of course, depending on the requirements,
assuming what I wrote is correct, performances
might be different.

I was just wondering if anybody has some hints,
some experience, some references, or, as you
suggested, not to care at all.

Thanks again,

bye,

-- 

piergiorgio