Debian Bug report logs - #686097
Can't make btrfs raid1 from installer

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Message #5 received at [email protected] (full text, mbox, reply):

From: Daniel Pocock <[email protected]>

To: [email protected]

Subject: Can't make btrfs raid1 from installer

Date: Tue, 28 Aug 2012 16:08:58 +0200

Package: installation-reports

Image version: beta1 DVD amd64
http://cdimage.debian.org/cdimage/wheezy_di_beta1/amd64/iso-dvd/debian-wheezy-DI-b1-amd64-DVD-1.iso
Date: 28 August 2012



I successfully proceed through all steps up to partitioning

In the partitioning system, I create two logical volumes:

/dev/vg00/lv0
/dev/vg00/lv1

I then exit the LVM tool and in the main partitioning tool, I highlight
each of them, and designate both of them as btrfs and mount pount = /

I was expecting to create a RAID1, e.g. for the installer to run the
following command:

mkfs.btrfs \
    -m raid1 \
    -d raid1 \
  /dev/vg00/lv0 /dev/vg00/lv1

When I select `Finish...write to disk' I see the error "Identical mount
points for two file systems"

If I try to use the menu option "Configure software RAID", it only
offers the `md' RAID1 and not btrfs RAID1

There are probably several valid ways to handle this:

a) if user selects "Configure software RAID", they could be offered an
option to choose either md or btrfs style RAID

b) if user tries to assign several devices to the same mount point,
maybe they should see a prompt asking them if they want RAID1, RAID0,
etc (or if they just made a mistake and want to go back)

c) hack: maybe just ask the user if they want to drop into a shell and
create the filesystem using their own mkfs command?

This is likely to be a pain because the user can't easily RAID their
btrfs filesystem after it has been created (needs a 3.3 or later kernel
and new tools).  Therefore, it must be done from the installer, or from
a command line during the install phase.
https://btrfs.wiki.kernel.org/index.php/Balance_Filters

Message #12 received at [email protected] (full text, mbox, reply):

From: Daniel Pocock <[email protected]>

To: [email protected]

Subject: possible solution

Date: Thu, 30 Aug 2012 18:33:38 +0200

Suggested that any enhancement to support this for wheezy must be
non-disruptive and must not require changes to any strings that would
need to be translated.

The only way I see of supporting that for wheezy is described below:



Concept:

  * user can specify two partitions with the same mount point,
    provided they are both btrfs
  * partman-btrfs will recognise this special case and assume
    that RAID1 is desired
  * due to the requirement to avoid changing any text strings,
    this will happen silently and the user will not be
    prompted to choose RAID level or other possible choices
  * if filesystems are not btrfs, the normal error will appear


package partman-target
----------------------

  check.d/
    proper_mountpoints
    duplicate_labels
        same_mountpoint and same_label errors must be suppressed when
        this special case is detected

package partman-btrfs
---------------------

  commit.d/
    format_btrfs
        * must do a pre-screening of all filesystem specs
          and identify those that need RAID
        * format the normal filesystems first, and the RAID ones in a
          second pass

  fstab.d/
    btrfs
        * must do a pre-screening of all filesystem specs
          and identify those that need RAID
        * output the normal filesystems first
        * for the RAID filesystems, must mount by UUID= syntax
          (due to bug #612402)
          http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=612402
        * one possible technique is to just check UUID of each
          filesystem, and parse the resulting fstab output via uniq

Message #17 received at [email protected] (full text, mbox, reply):

From: Joey Hess <[email protected]>

To: Daniel Pocock <[email protected]>

Cc: [email protected]

Subject: Re: understanding/contributing to partman-btrfs

Date: Thu, 30 Aug 2012 16:07:06 -0400

[Message part 1 (text/plain, inline)]

Daniel Pocock wrote:
> I've described such a solution in the bug report:
> 
>  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=686097
> 
> If you think it is sensible (or if something looks obviously silly),
> could you comment on it?  I will hopefully have more time next week to
> play with it, but I'll let it sit there for a few days to see if
> anyone has comments about it.

I don't know if that's worth it, it'll be a feature that entirely lacks
discoverability for users.

> Anything more comprehensive than what I've described would require UI
> changes (e.g. prompting user for RAID level)

Of course, d-i already knows how to promt the user for the RAID level --
when setting up normal software RAID. Finding a way to make partman-md
also support btrfs raid seems like a nice approach, but I don't know how
it would work either in the UI or internally.

-- 
see shy jo

[signature.asc (application/pgp-signature, inline)]

Message #22 received at [email protected] (full text, mbox, reply):

From: Daniel Pocock <[email protected]>

To: Joey Hess <[email protected]>

Cc: [email protected]

Subject: Re: understanding/contributing to partman-btrfs

Date: Thu, 30 Aug 2012 22:36:22 +0200

On 30/08/12 22:07, Joey Hess wrote:
> Daniel Pocock wrote:
>> I've described such a solution in the bug report:
>>
>>  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=686097
>>
>> If you think it is sensible (or if something looks obviously silly),
>> could you comment on it?  I will hopefully have more time next week to
>> play with it, but I'll let it sit there for a few days to see if
>> anyone has comments about it.
> 
> I don't know if that's worth it, it'll be a feature that entirely lacks
> discoverability for users.
> 

Maybe not such a bad thing: the btrfs crew still insist it is experimental.

Just the other day I saw something about btrfs crashing the kernel when
all RAID elements are not present

Message #27 received at [email protected] (full text, mbox, reply):

From: Martin Steigerwald <[email protected]>

To: [email protected]

Subject: Installing with BTRFS RAID 1: State? Any plans for Stretch?

Date: Sun, 11 Sep 2016 21:54:53 +0200

Hello!

Any updates on this bug report?

Related to it:

Bug#686130: still not booting from BTRFS RAID 1 on two LVs out of the box
https://bugs.debian.org/686130

I still have my initramfs work-around in place.

Thanks,
-- 
Martin

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