Re: Does --write-behind= have to be done at create time?

2007-06-29 Thread Ian Dall
On Thu, 2007-06-28 at 23:22 +0930, Ian Dall wrote:
 I was wanting to try out the --write-behind option. I have a raid1
 with bitmaps and write-mostly enabled, which are all the pre-requisites,
 I think.
 
 It would be nice if you could tweak this parameter on a live array, but
 failing that, it is hard to see why it couldn't be done at assemble
 time. mdadm wont let me though.
 
 Is this a fundamental limitation?

Looking through the mdadm source code it seems like


case O(BUILD, WriteBehind):
case O(CREATE, WriteBehind): /* write-behind mode */

could be changed to 

case O(GROW, WriteBehind):
case O(BUILD, WriteBehind):
case O(CREATE, WriteBehind): /* write-behind mode */

and everything would be OK. I am completely new to this code though, so
I am I missing something?

If you already had a bitmap you would need to remove it first
(--bitmap=none) and then grow it back with writebehind set.

Ian

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Does --write-behind= have to be done at create time?

2007-06-28 Thread Ian Dall
I was wanting to try out the --write-behind option. I have a raid1
with bitmaps and write-mostly enabled, which are all the pre-requisites,
I think.

It would be nice if you could tweak this parameter on a live array, but
failing that, it is hard to see why it couldn't be done at assemble
time. mdadm wont let me though.

Is this a fundamental limitation?

A related question, if I do recreate the same array, with exactly the
same parameters (except for the write-behind value) will my data still
be OK?


-- 
Ian Dall [EMAIL PROTECTED]
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