How to extend raw device size manually?

Suppose I create a 1G raw device on linux with as ase 12.5 like:

DISK INIT

    NAME='mydevice',

    PHYSNAME='/dev/raw/raw1',

    VDEVNO=5,

    SIZE='1024000',

    VSTART=0,

    CNTRLTYPE=0,

    DSYNC=FALSE

go

then I install dbextend for this ase. then I can set this device as autoextend with:

sp_dbextend 'set', 'device', 'mydevice', '10%'   --if this cause any performance problem?

or

sp_dbextend 'set', 'device', 'mydevice', '1024M'

then I have question about this:

if sp_dbextend is able to extend another 1G for this device, how can I do it manually?