On Fri, Feb 04, 2011 at 02:27:38AM -0600, Stan Hoeppner wrote:

Keld Jørn Simonsen put forth on 2/4/2011 1:06 AM:

quoted

Well RAID1+0 is not the best combination available. I would argue that
raid10,f2 is significantly better in a number of areas.

I'd guess Linux software RAID would be lucky to have 1% of RAID deployments
worldwide--very lucky.  The other 99%+ are HBA RAID or SAN/NAS "appliances" most
often using custom embedded RTOS with the RAID code written in assembler,
especially in the case of the HBAs.  For everything not Linux mdraid, RAID 10
(aka 1+0) is king of the hill, and has been for 15 years+

Yes, you are right, Linux MD really has an advantage here:-)

quoted

quoted

Something smells bad here.  Does one of the RAID companies own a patent or
trademark on "RAID 10"?  I'll look into this.  It just doesn't make any sense
for RAID 10 to be omitted from the SNIA DDF but to be referenced in the manner
it is.

It looks like they do define all major basic RAID disk layouts. (except
raid10,f2 of cause) . RAID1+0 is a derived format, maybe that is out of
scope of the DDF standard.

"A secondary virtual disk is a VD configured using hybrid RAID levels like
RAID10 or RAID50. Its elements are BVDs."

So apparently their Disk Data Format specification doesn't include hybrid RAID
levels.  This makes sense, as the _on disk_ layout of RAID 10 is identical to
RAID 1.

Yes, raid10 is just a variation of RAID1, actually raid10,n2 is
identical on the disk to RAID1, eg for a 2 drive or 4-drive array.

We apparently need to be looking for other SNIA documents to find their
definition of RAID 10.  That is what started us down this tunnel isn't it?
We're so deep now there's no light and I can't see the path behind me anymore. ;)

I dont think SNIA defines RAID 10, which is a specific Linux MD thing.

For RAID1+0, I think it is covered by the DDF standard, as what DDF is
aimed at is defining formats on the disks to portably handle RAID. That
means that you can move a set of disks used in one manufacturer's 
configuration  to another make's  configuration, and it will still work.

And it will also work with RAID1+0, as the underlying RAID1 and RAID0
formats are defined in DDF. So no need to add specific RAID1+0
definitions. Also RAID1 may mean different layouts, like the "far" and
"offset" layouts, and it would mean an explosion of definitions of
RAID1+0 if you should name and standardize all of these variations of
RAID1+0 explicitely.

best regards
keld

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