Re: Reason for md raid 01 blksize limited to 4 KiB?

[NeilBrown <neilb@suse.de>]

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On Tue, 29 May 2012 11:30:27 +0200 Sebastian Riemer
<sebastian.riemer@profitbricks.com> wrote:

> On 28/05/12 06:05, NeilBrown wrote:
> > What do you mean by "doesn't work"?  Returns errors? crashes? hangs? kills
> > you cat?
> > 
> 
> dd with oflag=direct returned an IO error.

Odd.  Updating mdadm shouldn't affect that.

> 
> > It works for me.
> > 
> > When I use 32K direct writes to a RAID1, both underlying RAID0 arrays see
> > 64-sector writes.
> > 
> > (when I do normal buffered writes I see 8-sector writes which seems odd,
> >  but clearly md/RAID1 is allowing large writes through)
> > 
> 
> Now, I've updated mdadm to version 3.2.5 and it works like you've
> described it. Thanks for your help! But the buffered IO is what matters.
> 4k isn't enough there. Please inform me about changes which increase the
> size in buffered IO. I'll have a look at this, too.

I don't know.  I'd have to dive into the code and look around and put a few
printks in to see what is happening.

NeilBrown

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