'resync=PENDING', 'auto-read-only' on raid1 creation

'resync=PENDING', 'auto-read-only' on raid1 creation

[Ron Leach]

List, good afternoon,

I've recently needed to create a new raid1 array in an existing 
(non-raid) Debian Wheezy system.  The array has been created 
read-only, and resync is PENDING; I didn't expect either of these 
conditions.

Objective is to have an LVM built initially on mirrored unused 2TB 
drives, with a view to growing the LVM with mirrored 3TB drives in the 
future.  The Logical volume will be exported over NFS, and will serve 
as a repository for backups of other machines.  The approach I am 
following is, first, to create a raid1 array then, second, install an 
LVM over that array, making sure that I create the LVM such that it 
can be expanded.

(I think) I've created a raid1 on two empty and unpartitioned 2TB 
drives, but am not seeing the results that the wiki 
(https://raid.wiki.kernel.org/index.php/RAID_setup) seems to suggest.

# cat /proc/mdstat
reports

md0 : active (auto-read-only) raid1 sdc[1] sdb [0]'
1953383360 blocks super 1.2 [2/2] [UU]
resync=PENDING

This was the create command I used:

# mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc

I've read through man mdadm but had not expected 'auto-read-only', nor 
'resync=PENDING'.  Has something gone wrong, for some reason?  Or do I 
need, simply, to set the array to be read-write?  I wondered whether 
'create' does not 'start' the array, but it's reported as 'active', so 
I think the array is started.  I have not yet put a filesystem on the 
array, because I am not sure the creation is ok.

Grateful for any comment, and apologies for what must seem a very 
basic question,

regards, Ron

Re: 'resync=PENDING', 'auto-read-only' on raid1 creation

[Phil Turmel]

Hi Ron,

On 01/04/2014 08:28 AM, Ron Leach wrote:
> List, good afternoon,
> 
> I've recently needed to create a new raid1 array in an existing
> (non-raid) Debian Wheezy system.  The array has been created read-only,
> and resync is PENDING; I didn't expect either of these conditions.
> 
> Objective is to have an LVM built initially on mirrored unused 2TB
> drives, with a view to growing the LVM with mirrored 3TB drives in the
> future.  The Logical volume will be exported over NFS, and will serve as
> a repository for backups of other machines.  The approach I am following
> is, first, to create a raid1 array then, second, install an LVM over
> that array, making sure that I create the LVM such that it can be expanded.
> 
> (I think) I've created a raid1 on two empty and unpartitioned 2TB
> drives, but am not seeing the results that the wiki
> (https://raid.wiki.kernel.org/index.php/RAID_setup) seems to suggest.
> 
> # cat /proc/mdstat
> reports
> 
> md0 : active (auto-read-only) raid1 sdc[1] sdb [0]'
> 1953383360 blocks super 1.2 [2/2] [UU]
> resync=PENDING
> 
> This was the create command I used:
> 
> # mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc
> 
> I've read through man mdadm but had not expected 'auto-read-only', nor
> 'resync=PENDING'.  Has something gone wrong, for some reason?  Or do I
> need, simply, to set the array to be read-write?  I wondered whether
> 'create' does not 'start' the array, but it's reported as 'active', so I
> think the array is started.  I have not yet put a filesystem on the
> array, because I am not sure the creation is ok.
> 
> Grateful for any comment, and apologies for what must seem a very basic
> question,

"auto-read-only" is a safety measure that prevents any writes to an
array until something in the data area is written.  I don't remember the
rules MD uses to determine if any given assemble/create operation
qualifies, but it isn't an error.

Just perform pvcreate on the array as you intended, and that'll switch
the array to rw (and start the resync).

HTH,

Phil

Re: 'resync=PENDING', 'auto-read-only' on raid1 creation

[Wilson Jonathan]

On Sat, 2014-01-04 at 11:38 -0500, Phil Turmel wrote:

> 
> "auto-read-only" is a safety measure that prevents any writes to an
> array until something in the data area is written.  I don't remember the
> rules MD uses to determine if any given assemble/create operation
> qualifies, but it isn't an error.

That explains an issue I had when creating a brand new raid6 and it
failed to start a sync as I expected it to... I probably went round the
house to "fix" it and ended up using a "missing" then adding the missing
drive which started the sync.

I guess its one of the problems, that isn't, that "just happens" when
you start to keep too close an eye on things, such as a "watch
proc/mdstat" in another window where as before I probably would have
just created it, added a file system, and been none the wiser :-/

> 
> Just perform pvcreate on the array as you intended, and that'll switch
> the array to rw (and start the resync).
> 
> HTH,
> 
> Phil

Re: 'resync=PENDING', 'auto-read-only' on raid1 creation

[Ron Leach]

On 04/01/2014 16:38, Phil Turmel wrote:
>
> Just perform pvcreate on the array as you intended, and that'll switch
> the array to rw (and start the resync).
>

Yep, it did, and has done; thank you for the re-assurance, Ron