thank you i will try it
On 31.03.2016 17:50, Dan Ritter wrote:
> On Thu, Mar 31, 2016 at 12:18:19PM +0200, basti wrote:
>> 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?
>
> You can either specify a file, or the word "internal" which
> means it will be stored in the RAID metadata area. "internal"
> is almost always safer.
>
>> How does backup disk know that is must sync changes of last 14 days?
>> when backup disk one was connected one week ago?
>
> It doesn't. When you connect the "backup" disk as a mirror to
> the existing mirror, mdadm decides that it is a damaged disk and
> attempts to repair it. The bitmap might help speed this up.
>
>> Is it possible to use a bitmap in this situation?
>
> Yes, but you should experiment to see whether this actually
> helps.
>
> Personally, I would consider making the backup disks look like
> separate mdadm RAID-1 devices, and using rsync to copy changed
> data across to them. If speed were important, I would strongly
> consider buying a PCI or PCIe USB3 card and upgrading the
> external enclosure(s) to USB3.
>
> -dsr-
>
