From: John Crisp <john@reetspetit.net>
To: linux-raid@vger.kernel.org
Subject: Re: RAID 1 partition with hot spare shows [UUU] ?
Date: Wed, 18 Apr 2012 10:42:27 +0200 [thread overview]
Message-ID: <4F8E7E73.5070909@reetspetit.net> (raw)
In-Reply-To: <20120418091233.23d77dfc@notabene.brown>
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On 18/04/12 01:12, NeilBrown wrote:
> On Wed, 18 Apr 2012 00:42:54 +0200 John Crisp wrote:
>>
>> I don't understand how md1 shows [UUU] ??
>
> You have a RAID1 with 3 devices. What it difficult to comprehend
> about that.
Probably a misunderstanding of the terminology - in Hicksville where I
live mirrored usually just means a pair ;-)
> Each block is written to all three devices.
I didn't realise that a RAID 1 could have more than two devices. Most
documentation around always illustrates a RAID 1 with a pair of drives
and hence the confusion.
>
> You don't want that? Change it.
>
> mdadm --grow /dev/md1 --raid-disks=4
>
> now it has 4 devices - though one will be missing.
>
Logical if you know it (RAID 1) can have more devices.
> mdadm --grow /dev/md1 --raid-disks=2
Illogical naming if what you actually want to do is shrink the
array............ like many things in life, once you know, you know.
>
> now it has 2 devices. Actually that won't work until you mark one
> of the devices as failed, so
>
> mdadm /dev/md1 --fail /dev/sdc1 mdadm --grow /dev/md1
> --raid-disks=2
>
And there lies the answer to my problem. For that I can't thank you
enough !
>
> But maybe you really wanted a 3-disk RAID1 before - it is a
> configuration that certainly has a place.
>
No I didn't, but I now understand.
> Next you'll be telling me that a RAID5 cannot be made with just 2
> devices! :-)
Me ? I know jack ...... though I know one more thing than I did
yesterday, and that is good enough for me !
Many thanks for the assistance.
B. Rgds
John
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next prev parent reply other threads:[~2012-04-18 8:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-17 22:42 RAID 1 partition with hot spare shows [UUU] ? John Crisp
2012-04-17 23:12 ` NeilBrown
2012-04-18 7:42 ` David Brown
2012-04-18 8:42 ` John Crisp [this message]
2012-04-18 9:09 ` David Brown
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