new superblock and raid10 support in mdadm

new superblock and raid10 support in mdadm

[rich turner]

the latest source of mdadm has ANNOUNCE-1.7.0 which indicates there will
be a new superblock format. we are currently developing a process by
which we read the superblock ourselves and parse through the information
we need about the raid devices. our fear is that we develop the process
to read the superblock and then it changes, which could cause us to
completely rewrite the process.
if we develop a process based on the current superblock format, will it
still work with the new superblock format?
is there any documentation for the format of the old superblock and new
superblock?
will there be any indication within the superblock that indicates which
format the superblock is using?

ANNOUNCE-1.7.0 also indicated support for raid10. outstanding news!
while i understand this is still under development, we would like to
learn as much as we can about this support so that we can support it
when it is considered stable. any information you can provide is
helpful.

Re: new superblock and raid10 support in mdadm

[Neil Brown]

On Monday September 13, rich@storix.com wrote:
> the latest source of mdadm has ANNOUNCE-1.7.0 which indicates there will
> be a new superblock format. we are currently developing a process by
> which we read the superblock ourselves and parse through the information
> we need about the raid devices. our fear is that we develop the process
> to read the superblock and then it changes, which could cause us to
> completely rewrite the process.
> if we develop a process based on the current superblock format, will it
> still work with the new superblock format?

The old (current) super block format will continue to work and will
continue to be widely used.  It would be entirely appropriate that you
require people who use your tool/service to continue to use the old
format.  However I suspect it would not be a great burden for you to
support the new format as well if/when it became popular.

A new format is being supported because the old format has problems.
One is that it cannot work with devices larger than 2 Gigabytes (and I
have had a request from someone who wanted to include such a device in
an MD array).
Another is that it cannot support checkpointing of reconstruction in a
backwards compatible way (we have checkpointing of resync, but not
reconstruct).

If neither of these are a problem (and they won't be for many people)
then the old superblock format can and will still be used.

> is there any documentation for the format of the old superblock and new
> superblock?

Not in great detail.  include/linux/raid/md_p.h is probably the best
you will get.  When I finish new superblock support in mdadm, I will
probably add some documentation.


> will there be any indication within the superblock that indicates which
> format the superblock is using?

Definitely.  The "major_version" will be '1' for the new format, and
'0' for the old.

> 
> ANNOUNCE-1.7.0 also indicated support for raid10. outstanding news!
> while i understand this is still under development, we would like to
> learn as much as we can about this support so that we can support it
> when it is considered stable. any information you can provide is
> helpful.

The raid10 module is in 2.4.9-rc2 and will be in 2.4.9 when it gets
released. 
There is a comment at the top of drivers/md/raid10.c that briefly
describes the layout.  More documentation should appear in the next
mdadm release.

I include the mentioned comment below.

NeilBrown


/*
 * RAID10 provides a combination of RAID0 and RAID1 functionality.
 * The layout of data is defined by
 *    chunk_size
 *    raid_disks
 *    near_copies (stored in low byte of layout)
 *    far_copies (stored in second byte of layout)
 *
 * The data to be stored is divided into chunks using chunksize.
 * Each device is divided into far_copies sections.
 * In each section, chunks are laid out in a style similar to raid0, but
 * near_copies copies of each chunk is stored (each on a different drive).
 * The starting device for each section is offset near_copies from the starting
 * device of the previous section.
 * Thus there are (near_copies*far_copies) of each chunk, and each is on a different
 * drive.
 * near_copies and far_copies must be at least one, and there product is at most
 * raid_disks.
 */

Re: new superblock and raid10 support in mdadm

[Jurriaan]

From: Neil Brown <neilb@cse.unsw.edu.au>
Date: Tue, Sep 14, 2004 at 11:08:53AM +1000
> A new format is being supported because the old format has problems.
> One is that it cannot work with devices larger than 2 Gigabytes (and I
> have had a request from someone who wanted to include such a device in
> an MD array).

I presume you mean terabyte, but I'm not sure you don't mean petabyte or
something else very large?

> The raid10 module is in 2.4.9-rc2 and will be in 2.4.9 when it gets
> released. 

2.6.9 I presume?

> /*
>  * RAID10 provides a combination of RAID0 and RAID1 functionality.
>  * The layout of data is defined by
>  *    chunk_size
>  *    raid_disks
>  *    near_copies (stored in low byte of layout)
>  *    far_copies (stored in second byte of layout)
>  *
>  * The data to be stored is divided into chunks using chunksize.
>  * Each device is divided into far_copies sections.
>  * In each section, chunks are laid out in a style similar to raid0, but
>  * near_copies copies of each chunk is stored (each on a different drive).
>  * The starting device for each section is offset near_copies from the starting
>  * device of the previous section.
>  * Thus there are (near_copies*far_copies) of each chunk, and each is on a different
>  * drive.
>  * near_copies and far_copies must be at least one, and there product is at most

----------------------------------------------------------their

>  * raid_disks.
>  */

Good luck,
Jurriaan
-- 
If you hear muffled screams, consider it a request for beam out.
	Tom Paris in Voyager
Debian (Unstable) GNU/Linux 2.6.9-rc1-mm4 2x6209 bogomips load 0.14

Re: new superblock and raid10 support in mdadm

[Neil Brown]

On Tuesday September 14, thunder7@xs4all.nl wrote:
> From: Neil Brown <neilb@cse.unsw.edu.au>
> Date: Tue, Sep 14, 2004 at 11:08:53AM +1000
> > A new format is being supported because the old format has problems.
> > One is that it cannot work with devices larger than 2 Gigabytes (and I
> > have had a request from someone who wanted to include such a device in
> > an MD array).
> 
> I presume you mean terabyte, but I'm not sure you don't mean petabyte or
> something else very large?

Yes.  terabyte (2^(32+9) bytes is the max size)
> 
> > The raid10 module is in 2.4.9-rc2 and will be in 2.4.9 when it gets
> > released. 
> 
> 2.6.9 I presume?

You presume correctly.  I type poorly :-)

> >  * near_copies and far_copies must be at least one, and there product is at most
> 
> ----------------------------------------------------------their
> 

Would you believe that I deliberately put in those errors just to see
if anyone actually reads these comments..... no, I wouldn't either.

Thanks,
NeilBrown

RE: new superblock and raid10 support in mdadm

[BO MOON]

Hello,

I noticed some discussions on last September email log,
But I am not sure.

I tried to make RAID10 or RAID01. I could make it but
Problem is that I could not assemble it by "mdadm -As"
When the system is rebooted.

My "mdadm.conf" is

    DEVICE /dev/hd*
    ARRAY /dev/md0 level=raid1 num-devices=2 devices=/dev/hda4,/dev/hdc4
    ARRAY /dev/md1 level=raid1 num-devices=2 devices=/dev/hde4,/dev/hdg4
    ARRAY /dev/md2 level=raid0 num-devices=2 devices=/dev/md0,/dev/md1

My S/W revs are:

Linux 2.4.20
Mdadm 1.2.0

My HDD size are all greater than 120 GB.

I tried it manually, too: first assemble the RAID1: md0 and md1.
Then tried to assemble "md2" but it said "could not find devices for
md2"

We do not support RAID10 or RAID01 on linux2.4.xx?  
or any issues on mdadm? 

Please provide me any clues or advices,

Bo

RE: new superblock and raid10 support in mdadm

[BO MOON]

Hello again,

I will re-iterate my question for raid10 or raid01.
1.  Is raid10.c in ONLY linux2.6.xx? no support for 2.4.xx?
2.  Does raid10.c support for RAID10 only? Or for both raid10 and
raid01?
3.  we can build raid10 or raid01 on linux2.4.xx without raid10.c code.
    What issues or bugs does this code take care of?
4.  What rev of mdadm should be used for raid10? Mdadm1.7 or greater?


Thx,

Bo

-----Original Message-----
From: BO MOON [mailto:bmoon@anthologysolutions.com] 
Sent: Wednesday, December 22, 2004 10:59 AM
To: 'Neil Brown'; 'rich turner'
Cc: 'linux-raid@vger.kernel.org'
Subject: RE: new superblock and raid10 support in mdadm

Hello,

I noticed some discussions on last September email log,
But I am not sure.

I tried to make RAID10 or RAID01. I could make it but
Problem is that I could not assemble it by "mdadm -As"
When the system is rebooted.

My "mdadm.conf" is

    DEVICE /dev/hd*
    ARRAY /dev/md0 level=raid1 num-devices=2 devices=/dev/hda4,/dev/hdc4
    ARRAY /dev/md1 level=raid1 num-devices=2 devices=/dev/hde4,/dev/hdg4
    ARRAY /dev/md2 level=raid0 num-devices=2 devices=/dev/md0,/dev/md1

My S/W revs are:

Linux 2.4.20
Mdadm 1.2.0

My HDD size are all greater than 120 GB.

I tried it manually, too: first assemble the RAID1: md0 and md1.
Then tried to assemble "md2" but it said "could not find devices for
md2"

We do not support RAID10 or RAID01 on linux2.4.xx?  
or any issues on mdadm? 

Please provide me any clues or advices,

Bo

RE: new superblock and raid10 support in mdadm

[Neil Brown]

On Wednesday December 22, bmoon@anthologysolutions.com wrote:
> Hello,
> 
> I noticed some discussions on last September email log,
> But I am not sure.
> 
> I tried to make RAID10 or RAID01. I could make it but
> Problem is that I could not assemble it by "mdadm -As"
> When the system is rebooted.
> 
> My "mdadm.conf" is
> 
>     DEVICE /dev/hd*
>     ARRAY /dev/md0 level=raid1 num-devices=2 devices=/dev/hda4,/dev/hdc4
>     ARRAY /dev/md1 level=raid1 num-devices=2 devices=/dev/hde4,/dev/hdg4
>     ARRAY /dev/md2 level=raid0 num-devices=2 devices=/dev/md0,/dev/md1
> 
> My S/W revs are:
> 
> Linux 2.4.20
> Mdadm 1.2.0
> 
> My HDD size are all greater than 120 GB.
> 
> I tried it manually, too: first assemble the RAID1: md0 and md1.
> Then tried to assemble "md2" but it said "could not find devices for
> md2"

That would be because /dev/md0 and /dev/md1 aren't listed in "DEVICE"
lines.

NeilBrown

> 
> We do not support RAID10 or RAID01 on linux2.4.xx?  
> or any issues on mdadm? 
> 
> Please provide me any clues or advices,
> 
> Bo
> 

RE: new superblock and raid10 support in mdadm

[Neil Brown]

On Wednesday December 22, bmoon@anthologysolutions.com wrote:
> Hello again,
> 
> I will re-iterate my question for raid10 or raid01.
> 1.  Is raid10.c in ONLY linux2.6.xx? no support for 2.4.xx?

2.6 only

> 2.  Does raid10.c support for RAID10 only? Or for both raid10 and
> raid01?

raid10.c supports an arrangement where data is both striped and
mirrored. 
The difference between raid1+0 and raid0+1 (which also both stripe and
mirror) is not relevant when the striping and mirroring is done in the
one module.


> 3.  we can build raid10 or raid01 on linux2.4.xx without raid10.c code.
>     What issues or bugs does this code take care of?

raid10.c provides more flexibility and simpler management.

> 4.  What rev of mdadm should be used for raid10? Mdadm1.7 or greater?
> 

Should work with 1.7.0, but would recommend upgrading to 1.8.0 anyway
(NOT 1.8.1).

NeilBrown