[linux-lvm] Using Oracle with lvm AND rawio: read(512) from

[Andreas Dilger]

Michael Tokarev writes:
> What's *still* unknown to me is a difference between character and
> block specials.  In principle, block device should only allow
> block access (i.e. multiple of 512 or 1024 or whatether size),
> while character devs should allow read of 1 byte.

Actually, it is just the opposite for devices like hard drives:
the block interface will read a whole block no matter what size of
I/O you do, and it will cache the block for any smaller read/write
actions (i.e. read whole block-modify part of block-write whole block).
The character interface do NOT buffer the data, so the application
is forced to do correct block-sized and aligned reads/writes themselves.
The benefit of the character device is that it doesn't do cacheing.

> but for shure this isn't a solution, since we'll not be able
> to extend that datafile from oracle (like extending filesystem
> on top of lv), since this again will require writing/reading
> like at initial creation time, -- so almost all lvm work will
> go away.

You don't have to extend the datafiles for Oracle, just add a new
datafile to the tablespace.

Cheers, Andreas
-- 
Andreas Dilger                               TurboLabs filesystem development