Re: how to clone a disk

[Ming Zhang <mingz@ele.uri.edu>]

On Sat, 2006-03-11 at 16:31 -0800, dean gaudet wrote:
> On Sat, 11 Mar 2006, Ming Zhang wrote:
> 
> > On Sat, 2006-03-11 at 16:15 -0800, dean gaudet wrote:
> > 
> > > you're planning to do this while the array is online?  that's not safe... 
> > > unless it's a read-only array...
> > 
> > what i plan to do is to pull out the disk (which is ok now but going to
> > die), so raid5 will degrade with 1 disk fail and no spare disk here,
> > then do ddresue to a new disk which will have same uuid and everything,
> > then put it back, then bitmap will shine here right?
> > 
> > so raid5 is still online while that disk is not part of raid5 now. and
> > no diskio on it at all. so do not think i need an atomic operation here.
> 
> if you fail the disk from the array, or boot without the failing disk, 
> then the event counter in the other superblocks will be updated... and the 
> removed/failed disk will no longer be considered an up to date 
> component... so after doing the ddrescue you'd need to reassemble the 
> raid5.  i'm not sure you can convince md to use the bitmap in this case -- 
> i'm just not familiar enough with it.

i am little confused here. then what the purpose of that bitmap for? is
not that bitmap is for a component temporarily out of place and thus out
of sync a bit?

> 
> > this raid5 over raid1 way sounds interesting. worthy trying.
> 
> let us know how it goes :)  i've considered doing this a few times 
> myself... but i've been too conservative and just taken the system down to 
> single user to do the ddrescue with the raid offline entirely.

sure. after we finish this discussion and sort out a stable plan. do not
want to risk my data. :P

> 
> -dean