Re: man mdadm regarding --assume-clean says it's OK to use with RAID1 or 10, when creating:

[Neil Brown <neilb@suse.de>]

On Sunday August 23, for.poige+linux@gmail.com wrote:
> 2009/8/23 NeilBrown <neilb@suse.de>:
> [...]
> > Yes it will be updated.  But if it is updated with a
> > read-modify-write cycle then an old incorrect value will be updated
> > to a new incorrect value, which doesn't help you much.
> 
> 	I see. Thank you for the answer. My assumption was due thinking that
> parity is never being used when RAID5 is in "healthy" mode.
> 	
> 	But anyway, please clear it up: if I've made --asume-clean RAID5
> array, formatted it with some FS (or even LVM), and put OS/data to it,
> then (in idle at night, for e. g.) run "resync", would that be the
> same valid result (overall data integrity) as if I had previously
> created it without "--asume-clean" at all? (Let's suppose hard disks
> were healthy in both cases :-)

If by 'run "resync"' you mean
   echo repair > /sys/block/mdXX/md/sync_action
then yes, what will have the same effect as not using --assume-clean
to start with.

> 
> 	And Neil, using the chance to have your reply :-) I'd like to ask one
> more question: is that true (I think and hope it is!) that MD doesn't
> read/write full chunk size when it's just to read/write another block
> of data and hence chunk size only affects data interleaving on disks.

That is correct - chunk size only affect data layout, not IO size.
md/raid5 always reads or writes a whole page (normally 4K) at a time.

NeilBrown


> 	
> 	P. S. Is there someone on this list who can share his linux-RAID
> archive in mbox format? From time to time I find interesting
> discussions have been going but can't just hit "Reply". If you can
> help me with that, please reply personally (not CC:ing to the list).
> Thanks!
> 
> -- 
> End of message. Next message?
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