[dm-devel] kernel 2.6 biosraid via device mapper - partition support

[Don Mulvey]

>> Sounds like you should look at the EVMS activate command.  EVMS can
already
>> recognize and activate/reactivate: os/2, dos, bsd (compatible and
>> dedicated), solarisx86(embedded), unixware(embedded), 390 (cdl,ldl,cms),
>> mac, cluster and bbr partitions throught its device mapper interface.

>... you mean by attaching the dos-plugin segment manager? at first i was
>not sure if it actually parses the partition table or just writes its so
>that other OSes can also access the disk. but according to the user

The evms dos plug-in functions like fdisk in that it is able to
create/delete/resize/move dos partitions. It also recognizes embedded
solarisx86, bsd and unixware partitions.  Further, it recognizes and
maintains os/2 dlat tables.  Further still ... it will create and maintain
dm linear maps for these partitions.

>guide it would work just fine for this application.
>there is one thing that worries me. in capter "6.3. Adding a segment
>manager to an existing disk" there is the following sentence:

><quote>
>... Metadata sectors are written to disk to save information needed by
>the segment manager; previous information found on the disk is lost. ...
></quote>

>what is meant by metadata? evms private data or the dos partition table?
>where on the disk (segment?) is this information stored? for example i
>cannot use this if sector 9 is overwritten with metadata because of this
>would destroy the raid signature.

Most every plug-in uses some kind of metadata and evms seldom makes it up.
The dos plug-in uses MBR and EBR sectors for creating dos partitions.  It
will also maintain os/2 drivelink-address-tables (dlats) if they are found.
It didn't create any new metadata because it would not be compatible with
any other dos partitioning utility like fdisk.  In short ... the MBR is LBA
0 and OS/2 dlats are the last sector of every MBR and EBR track.  An
extended partition is specified in the MBR partition table and the very
first sector of the extended partition (cyl alligned) will have an EBR that
anchors the EBR chain ... and so forth.

-Don