Re: changing raid level?

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> The weird part: I then used -i, and started watching with raidctl
>> -S.  Based on the ETAs, the -i rebuild is happening about five times
>> as fast as it was when I did destroy the beginning of the disks [...]
> My guess is it slowed down significantly again...

Turns out yes, it did.

> The basic algorithm used for this is:

>   read unit from component A, read unit from component B
>   If data read is different, then write what was read from A onto B.

Heh.  Raidframe keeps surprising me.  That would explain it; it was
very fast while reading the portion that the previous run updated.

I was expecting this would be a simple "copy from A to B" operation; I
guess someone (a) optimized for the common case of almost-up-to-date
and (b) thinks reads are better (faster, or whatever) than writes.
Next time I have occasion to add a not-nearly-up-to-date member to a
raid 1, I'll copy data myself first.  (I have a program that copies
data rather like simple use of dd, but overlaps reads and writes for
better speed - and in many cases it does run substantially faster.)

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