Re: Triple parity and beyond

[Alex Elsayed <eternaleye@gmail.com>]

Stan Hoeppner wrote:

> On 11/23/2013 11:14 PM, John Williams wrote:
>> On Sat, Nov 23, 2013 at 8:03 PM, Stan Hoeppner <stan@hardwarefreak.com>
>> wrote:
<snip>
> 
>> 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.