On Jan 14, 2009, at 2:05 PM, Bjørn Vermo wrote:
On 14. jan.. 2009, at 12.17, Jasse Jansson wrote:
First of all, thanks Simon for the links, It sure was interesting
reading.
On Jan 14, 2009, at 11:45 AM, Bjørn Vermo wrote:
I have toyed with the idea that one drive in a mirrored pair
ought to have the addresses inverted, so sector 1 on one drive is
mapped to sector MAX -1 on the other.
I read it like the locality (radius) of the errors occur on the
same disc,
so I don't see the benefit from your "reversed mirror strategy".
He clearly stated that some drives models had error spikes at
certain cluster numbers.
This should not really surprise anybody who is familiar with the
way modern drives work internally. The cylinder where you change to
a different data density is a border case, and any border cases
open extra bug opportunities.
That's true.
You will also get some interesting performance problems to tackle,
when
one disc works on the inner tracks and the other one is on the
outer tracks.
A smart controller could make that into an opportunity. It is
hardly any more difficult than staggered stripes, which is widely
implemented.
In most mirroring controllers I have seen the system will get the
read data from the first drive that has them ready. Two "opposite"
drives should be able to offer a better average read performance.
Sure, reads is no problem.
I was thinking about write performance and possible sync windows,
but I didn't spell it out. My bad.
Kaiser Jasse -- Authorized Stealth Oracle
The axioms of wisdom:
1. Go the SPARC way of life
2. You can't conquer the universe without the knowledge of FORTRAN
3. In the Unix realm, 10% of work fixes 90% of the problems
