David Brown wrote:

One thing to watch out for when making high-availability systems and 
using RAID1 (or RAID10), is that RAID1 only tolerates a single failure 
in the worst case.  If you have built your disk image spread across 
different machines with two-copy RAID1, and a server goes down, then 
the rest then becomes vulnerable to a single disk failure (or a single 
unrecoverable read error).

It's a different matter if you are building a 4-way mirror from the 
four servers, of course.

Just a nit here: I'm looking at "md RAID10" which behaves quite 
differently that conventional RAID10.  Rather than striping and raiding 
as separate operations, it does both as a unitary operation - 
essentially spreading n copies of each block across m disks.  Rather 
clever that way.

Hence my thought about a 16-disk md RAID10 array - which offers lots of 
redundancy.

Miles

-- 
In theory, there is no difference between theory and practice.
In<fnord>  practice, there is.   .... Yogi Berra