About re-adding disk to raid which havent' bitmap

About re-adding disk to raid which havent' bitmap

[majianpeng]

Hi Neil,
	At present, re-add operation only useful raid which had bitmap.
	Through the git-log, i found the commit:
>commit 07d84d109d8beedd68df9da2e4e9f25c8217e7fb
>Author: NeilBrown <neilb@suse.de>
>Date:   Mon Jun 26 00:27:56 2006 -0700
>    [PATCH] md: Allow re-add to work on array without bitmaps
 >   When an array has a bitmap, a device can be removed and re-added and only
 >   blocks changes since the removal (as recorded in the bitmap) will be resynced.    
 >   It should be possible to do a similar thing to arrays without bitmaps.  i.e.
 >   if a device is removed and re-added and *no* changes have been made in the
 >   interim, then the add should not require a resync.    
 >   This patch allows that option.  This means that when assembling an array one
 >   device at a time (e.g.  during device discovery) the array can be enabled
 >   read-only as soon as enough devices are available, but extra devices can still
 >   be added without causing a resync.

Q1:why you think " if a device is removed and re-added and *no* changes have been made in the
   interim, then the add should not require a resync."?
Q2: Whether intentional or not, remove the device will cause the event of raid changed.So for raid which haven't bitmap,
re-add must failed and only added which cause recovery.
	For ssd, recovery will write whole disk.But if user used re-add parameter, he/she know the different of data.So i think it should do something for this.
	
	

Thanks!
Jianpeng