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@xxxxxxx>
>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
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