Re: Triple parity and beyond

Stan Hoeppner wrote:

On 11/23/2013 11:14 PM, John Williams wrote:

quoted

On Sat, Nov 23, 2013 at 8:03 PM, Stan Hoeppner [off-list ref]
wrote:

<snip>

quoted

But I, and a number of other people I have talked to or corresponded
with, have had mdadm RAID 5 or RAID 6 rebuilds of one drive run at
approximately the optimal sequential write speed of the replacement
drive. It is not unusual on a reasonably configured system.

I freely admit I may have drawn an incorrect conclusion about md parity
rebuild performance based on incomplete data.  I simply don't recall
anyone stating here in ~3 years that their parity rebuilds were speedy,
but quite the opposite.  I guess it's possible that each one of those
cases was due to another factor, such as user load, slow CPU, bus
bottleneck, wonky disk firmware, backplane issues, etc.

Well, there's also the issue of selection bias - people come to the list and 
complain when their RAID is taking forever to resync. People generally don't 
come to the list and complain when their RAID resyncs quickly and without 
issues.