Re: XFS on top RAID10 with odd drives count and 2 near copies

On Wed, Feb 15, 2012 at 01:10:32PM +0100, David Brown wrote:

Reads will normally be taken from the outer halves (A1 and B1), since 
these have faster throughput, and keeping the heads there means half the 
head movement (actually less than that on average).  But if the system 
happens to be reading from (or writing to) A1, and needs access to data 
that is also on A1, it can read it from B2 in parallel.

reads in raid10,far will allways come from the lowest block available disk,
that is the fastest disk on most hardware disks. This is to prevent
oddly characteriscs disks from not striping: when two disks with eg slightly
different access times were read from, the IO driver could tend to favourize
the faster, and thus make overall operations slower. This also works in
degraded mode. I wrote the one-line patch:-)

Best regards
Keld