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Date: Tue, 23 Sep 2014 21:21:24 -0500
From: Eric Sandeen <sandeen@sandeen.net>
MIME-Version: 1.0
Subject: Re: How to format RAID1 correctly
References: <5422146A.90206@evermeet.cx> <54222763.40107@sandeen.net>
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To: Helmut Tessarek <tessarek@evermeet.cx>, xfs@oss.sgi.com

On 9/23/14 9:11 PM, Helmut Tessarek wrote:
> On 23.09.14 22:07 , Eric Sandeen wrote:
>> but!  your raid doesn't have a 64k stripe, so that doesn't apply.
> 
> Yep, that's true, but see below.
> 
>> no geometry because md0 raid1 doesn't export any stripe geometry.
> 
> [root@atvie01s ~]# cat /proc/mdstat
> Personalities : [raid1]
> md0 : active raid1 sdb1[0] sdd1[1]
>       3906784064 blocks super 1.2 [2/2] [UU]
>       bitmap: 0/30 pages [0KB], 65536KB chunk
> 
> So for some reason it shows a 64k chunk size even for RAID1.
> 
> That was what got me confused.

Hm, 65536KB sounds like 64MB...

Anyway, mkfs.xfs picks up the queue's minimum IO size for
sunit, and optimal io size for swidth.

So:

blkid # blockdev --getiomin --getioopt /dev/md0 

(which here returns:
512
0
here)

will show you what your raid's queue is actually reporting,
and what mkfs.xfs will pick up.

-Eric




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