Adding a bitmap, v 0.90 superblocks

Adding a bitmap, v 0.90 superblocks

[Richard Michael]

I would like to add an internal bitmap to my RAID1 array.  It uses
v 0.90 superblocks.

Reading the man page, I believe I do this with:

"mdadm --grow --bitmap=internal /dev/mdX"

correct?

How do I know how much space is available on the superblock when mdadm
will perform it's computation "to make best use of available space"?
I'm curious because perhaps I should change to 1.x superblocks in the
future (for non-bootable arrays).

Regards,
Richard

Re: Adding a bitmap, v 0.90 superblocks

[Neil Brown]

On Tuesday July 29, rmichael-raid@edgeofthenet.org wrote:
> I would like to add an internal bitmap to my RAID1 array.  It uses
> v 0.90 superblocks.
> 
> Reading the man page, I believe I do this with:
> 
> "mdadm --grow --bitmap=internal /dev/mdX"
> 
> correct?

Correct!

> 
> How do I know how much space is available on the superblock when mdadm
> will perform it's computation "to make best use of available space"?
> I'm curious because perhaps I should change to 1.x superblocks in the
> future (for non-bootable arrays).

with 0.90, there is about 60K guaranteed to be available.  This is
491520 bits.

With 1.0 there 3K guaranteed to be available, though there might be
more.  I don't think we use the "more" currently unless you add a
bitmap when creating the array.

So there is no need to change metadata version for more bitmap space.

NeilBrown