mdadm Write-intent bitmap

[basti <black.fledermaus@arcor.de>]

Hello,

I have a mdadm software raid with 3 disks so far so good.

One disk (No. 3) is my backup disk which is connected once a week.
I have also a 2'nd Backup disk so one week backup disk 1 is connected to
other week backup disk 2 then backup disk 1 again and so on)

Now I want to use an internal "Write-intent bitmap" because I update my
array to 2 TB disks and there is only USB 2 which takes to long to sync
the disks.

Where is the bitmap saved?
How does backup disk know that is must sync changes of last 14 days?
when backup disk one was connected one week ago?

Is it possible to use a bitmap in this situation?

Best regards,
basti