The effects of multiple layers of block drivers

The effects of multiple layers of block drivers

[Dennison Williams]

Hello,

I am starting to dig into the Block subsystem to try and uncover the
reason for some data I lost recently.  My situation is that I have
multiple block drivers on top of each other and am wondering how the
effectss of a raid 5 rebuild would affect the block devices above it.

The layers are raid 5 -> lvm -> cryptoloop.  It seems that after the
raid 5 device was rebuilt by adding in a new disk, that the cryptoloop
doesn't have a valid ext3 partition on it.

As a raid device re-builds is there ant rearranging of sectors or
corresponding blocks that would effect another block device on top of it?

Sincerely,
Dennison Williams

Re: The effects of multiple layers of block drivers

[Neil Brown]

On Thursday January 10, evoltech@2inches.com wrote:
> Hello,
> 
> I am starting to dig into the Block subsystem to try and uncover the
> reason for some data I lost recently.  My situation is that I have
> multiple block drivers on top of each other and am wondering how the
> effectss of a raid 5 rebuild would affect the block devices above it.

It should "just work" - no surprises.  raid5 is just a block device
like any other.  When doing a rebuild it might be a bit slower, but
that is all.

> 
> The layers are raid 5 -> lvm -> cryptoloop.  It seems that after the
> raid 5 device was rebuilt by adding in a new disk, that the cryptoloop
> doesn't have a valid ext3 partition on it.

There was a difference of opinion between raid5 and dm-crypt which
could cause some corruption.
What kernel version are you using, and are you using dm-crypt or loop
(e..g losetup) with encryption?


> 
> As a raid device re-builds is there ant rearranging of sectors or
> corresponding blocks that would effect another block device on top of it?

No.

NeilBrown

Re: The effects of multiple layers of block drivers

[Nagilum]

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----- Message from evoltech@2inches.com ---------
     Date: Thu, 10 Jan 2008 14:58:49 -0800
     From: Dennison Williams <evoltech@2inches.com>
Reply-To: Dennison Williams <evoltech@2inches.com>
  Subject: The effects of multiple layers of block drivers
       To: linux-raid@vger.kernel.org


> Hello,
>
> I am starting to dig into the Block subsystem to try and uncover the
> reason for some data I lost recently.  My situation is that I have
> multiple block drivers on top of each other and am wondering how the
> effectss of a raid 5 rebuild would affect the block devices above it.
>
> The layers are raid 5 -> lvm -> cryptoloop.  It seems that after the
> raid 5 device was rebuilt by adding in a new disk, that the cryptoloop
> doesn't have a valid ext3 partition on it.
>
> As a raid device re-builds is there ant rearranging of sectors or
> corresponding blocks that would effect another block device on top of it?
>
> Sincerely,
> Dennison Williams

----- End message from evoltech@2inches.com -----

If you add a disk and do a reshape the layer on top of the raid5  
should only notice that the device is larger now. But yes, there is a  
rearranging of sectors going on. However this is transparent to layers  
on top.
Did you have a disk failure during the reshape? If yes you probably  
have been bitten by the same bug as me:  
(http://marc.info/?l=linux-raid&m=119910305111460&w=2).
Kind regards,

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