Re: Is there any lazy initialization mechanism in linux-raid?

[NeilBrown <neilb@suse.com>]

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On Fri, Dec 15 2017, guomingyang wrote:

> Hi all:
>
>        Today's disk is becoming larger and larger, and the recovery time 
> is becoming longer. I'm thinking about a lazy initialization mechanism 
> in linux raid5 to speed up recovery, which contains an un-initializing 
> bitmap and a backend thread for initializing stripes lazily only after a 
> stripe is write. The major difference is as follows:
>
>        (1)When a raid4 or raid5 device is created, we don't recovery a 
> disk as usual, instead we just set all the bit in un-initialize bitmap.
>
>        (2)When a write happens and the corresponding un-initializing bit 
> is set, we must first clean the bit, then wake up the backend thread to 
> resync the stripe, and only do RCW in corresponding stripe before the 
> resync is done.
>
>       The major advantage of this mechanism is that when a disk is 
> replaced, we can only recovery the stripes which have been initialized, 
> so as to speed up recovery.
>
>       Does linux-raid have similar mechanism today? Or is there anyone 
> who has already working on similar mechanism?
>

No, linux-raid doesn't support this.
I don't know of anyone working on this.
I wrote about the idea nearly 7 years ago

   http://neil.brown.name/blog/20110216044002#5

but never got around to doing anything.  It probably wouldn't be too
hard if someone wanted it enough to put in some effort.

NeilBrown


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