On Mon, 14 Jun 2010 17:53:27 +0600 Roman Mamedov <roman@xxxxxxxx> wrote: > On Mon, 14 Jun 2010 19:47:42 +1000 > Neil Brown <neilb@xxxxxxx> wrote: > > > When you create an array an specify that a bitmap be added at the same time, > > there is more flexibility for size and location of the bitmap. It can easily > > be more that 3K in that case. > > > > So presumably this array was created with a bitmap, rather than created > > without a bitmap and had a bitmap added later with --grow. Correct? > > Yes, as far as I remember. However, it seems a bit unfortunate to have any > significant difference between adding the bitmap right when creating the > array, and adding it later. For that reason, I'd suggest reserving more space > in the metadata than 3K, even if the bitmap isn't requested - and even if it > won't be added later, then that space could prove useful for something else > that might require it later. Maybe 64, 128 or 256K - still miniscule compared > to the array size, and could provide some nice flexibility for the future. > Yes. An I'm fairly sure mdadm does always reserve space. The point is that (until very recently) it wasn't possible to tell the kernel where to add a bitmap to an active array - just that it should add one. So it could only add it at a place that it was certain would be usable. That is the place I described. It is now possible to give the kernel more details of the bitmap to add. I just need to teach mdadm how to choose the best space and how to tell the kernel about it. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
