no matter what raid1 or raid10 system we use
raid1 is mirror! let´s think that raid0 = more than one disk (not a
single disk)...

if a hard disk inside a mirror (raid1) fail (it can be a raid0 or a
single disk) the mirror is failed
for example: there´s no 25% survival for 2 mirrors with 4 disks!
probability, here, is mirror based, not disk based!
it´s not a question about linux implementation is a question for
generic raid1 (mirror) system (1 failed 2 mirrors = 1 mirror failed
but 1 mirror working)

you only can have 25% 'survival' if you can use 4 disks, or multiples
of 4, for raid1
if your raid0 is broken you don´t have a raid0! you have a broken raid
= broken mirror (for raid1)!

should i write it again? for raid10 (raid1+0) with 4 disks you can
only lost 1 disk! 1 disk lost = 1 raid0 lost = 1 mirror lost!
should i write it again?

2011/1/31 Keld Jørn Simonsen [off-list ref]:

On Mon, Jan 31, 2011 at 02:17:37PM -0600, Stan Hoeppner wrote:

quoted

Keld Jørn Simonsen put forth on 1/31/2011 1:28 PM:

quoted

Top-posting...

How is the raid0+1 problem of only 33 % survival for 2 disk with RAID10?

I know for RAID10,F2 the implementation in Linux MD is bad.
It is only 33 % survival, while it with a probably minor fix could be 66%.

But how with RAID10,n2 and RAID10,o2?

I don't care what Neil or anyone says, these "layouts" are _NOT_ RAID 10.  If
you want to discuss RAID 10, please leave these non-standard Frankenstein
"layouts" out of the discussion.  Including them only muddies things unnecessarily.

Please keep terminology clean, and non-ambigeous.
Please refer to the old term RAID10 as RAID1+0, which is also the
original and more precise term for that concept of multilevel RAID.

RAID10 on this list refers to the RAID10 modules of the Linux kernel.

I can concurr that this may be a somewhat misleading term, as it is
easily confused with the popular understanding of RAID10, meaning
RAID1+0. And I see Linux RAID10 as a family of RAID1 layouts.
Indeed RAID10,n2 is almost the same as normal RAID1, and RAID10,o2
is an implementation of a specific layout of the RAID1 standard.
RAID10,f2 could easily also be seen as a specific RAID1 layout.

But that is the naming of terms that we have to deal with on this Linux
kernel list for the RAID modules.

best regards
Keld
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-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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