Re: [RFCI] How best to partition MD/raid devices in 2.6

On Friday November 14, dang@fprintf.net wrote:

On Thu, 2003-11-13 at 22:11, Neil Brown wrote:

quoted

RFCI == Request For Clever Ideas.

Hi all..

 I want be able to partition "md" raid arrays.
 e.g. I want to be able to use RAID1 to mirror sda and sdb as whole
 drives, and then partitions that into root, swap, other (or whatever
 suits the particular situation).

<snip>

Can't LVM do this?  I have a raid array (mirror) that is LVM'd into
multiple partitions.  It currently runs 2.4, but it should work fine
with 2.6, right?  All the rest of my boxes have 2.6 and LVM, but no raid
(no duplicate hard drives).

Fair question.
I want it to work with "standard" partition tables such as MSDOS
partitions etc.
I would like to be able to take a single drive that is being used and
has partitions on it, and to add an identical drive beside it, mirror
them, and get a mirrored pair that looked much like the original
drive.
There are issues with the raid superblock but assuming they can be
solved, I want partitioning to work easily.

Can LVM work happily with 'legacy' partitioning information?

NeilBrown

On 2003-11-14T16:30:42,
   Neil Brown [off-list ref] said:

There are issues with the raid superblock but assuming they can be
solved, I want partitioning to work easily.

Can LVM work happily with 'legacy' partitioning information?

I'd really suggest to run DM (either LVM2 or EVMS2) on top of md
instead. It's much more flexible; I don't see any benefit in 'old style'
partition information, which has all sorts of problems - ie,
non-transactional updates (_why_ were you running raid again? ;), static
as they can't be modified during runtime etc.


Sincerely,
    Lars Marowsky-Brée [off-list ref]

-- 
High Availability & Clustering	      \ ever tried. ever failed. no matter.
SUSE Labs			      | try again. fail again. fail better.
Research & Development, SUSE LINUX AG \ 	-- Samuel Beckett

On Fri, Nov 14, 2003 at 11:16:47AM +0100, Lars Marowsky-Bree wrote:

On 2003-11-14T16:30:42,
   Neil Brown [off-list ref] said:

quoted

There are issues with the raid superblock but assuming they can be
solved, I want partitioning to work easily.

Can LVM work happily with 'legacy' partitioning information?

I'd really suggest to run DM (either LVM2 or EVMS2) on top of md
instead. It's much more flexible; I don't see any benefit in 'old style'
partition information, which has all sorts of problems - ie,
non-transactional updates (_why_ were you running raid again? ;), static
as they can't be modified during runtime etc.

This brings up a tangent point...  partitions on top of RAID are a new
thing, which means that one has the chance to define the partition
format.

And I kinda like EFI partition format, a lot better than the other
common ones...

	Jeff


P.S. No, this isn't a blanket endorsement of EFI as a whole :)

My hard disks support some programmable options.

Automatic Write Reallocation Enable (AWRE):
  On, drive automatically relocates bad blocks detected during write
operations.  Off, drive creates Check Condition status with sense key of
Medium Error if bad blocks are detected during write operations.

Automatic Read Reallocation Enable (ARRE):
  On, drive automatically relocates bad blocks detected during read
operations.  Off, drive creates Check Condition status with sense key of
Medium Error if bad blocks are detected during read operations.

These options are both off.

Would md be happier if these were on?  This would hide recoverable errors
from md.

Any opinions?

My disks are ST118202LC.

Thanks.