Si recordamos, el truco de crear el raid 1 con un único disco no funcionaba para un raid lineal, así que, ¿qué podemos hacer?. La solución que se me ha ocurrido es usar LVM. Aunque no es exactamente un raid lineal el resultado final es el mismo puesto que tenemos un único punto de montaje y la capacidad de los dos discos.
Al igual que en el artículo anterior, no me voy a extender demasiado en los detalles puesto que mi anterior artículo sobre LVM en linux es más completo.
shian:~# fdisk /dev/sdb
...
Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 130 1044193+ 8e Linux LVM
...
shian:~# pvcreate /dev/sdb1
Physical volume "/dev/sdb1" successfully created
shian:~# vgcreate vg01 /dev/sdb1
Volume group "vg01" successfully created
shian:~# lvcreate -L 1G -n lvdatos vg01
Logical volume "lvdatos" created
shian:~# mkfs.ext3 /dev/vg01/lvdatos
shian:~# mkdir /mnt/datos_lvm
shian:~# mount /dev/vg01/lvdatos /mnt/datos_lvm/
shian:~# cp -a /mnt/datos/* /mnt/datos_lvm/
shian:~# df -h
/dev/sda1 1004M 43M 911M 5% /mnt/datos
/dev/mapper/vg01-lvdatos
1001M 18M 932M 2% /mnt/datos_lvm
shian:~# umount /dev/sda1
shian:~# fdisk /dev/sda
...
Disk /dev/sda: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 130 1044193+ 8e Linux LVM
shian:~# pvcreate /dev/sda1
Physical volume "/dev/sda1" successfully created
shian:~# vgextend vg01 /dev/sda1
Volume group "vg01" successfully extended
shian:~# vgdisplay -v vg01
Using volume group(s) on command line
Finding volume group "vg01"
--- Volume group ---
VG Name vg01
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 2
Act PV 2
VG Size 1.98 GB
PE Size 4.00 MB
Total PE 508
Alloc PE / Size 254 / 1016.00 MB
Free PE / Size 254 / 1016.00 MB
VG UUID fYT1oQ-w6zH-z6b6-58eo-qZ39-u1Ua-vROsN4
--- Logical volume ---
LV Name /dev/vg01/lvdatos
VG Name vg01
LV UUID NBOF9q-jmfW-RCik-MH2P-0Od4-DgMR-5YRJf7
LV Write Access read/write
LV Status available
# open 1
LV Size 1016.00 MB
Current LE 254
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:0
--- Physical volumes ---
PV Name /dev/sdb1
PV UUID yH8UHo-Vgy2-Pk9t-AozF-s1Ik-JPmL-og1kM4
PV Status allocatable
Total PE / Free PE 254 / 0
PV Name /dev/sda1
PV UUID 4cGeH2-nl7W-eH4a-mBHo-BCBI-b0np-f6gw1v
PV Status allocatable
Total PE / Free PE 254 / 254
shian:~# lvextend -L+1016M /dev/vg01/lvdatos
Extending logical volume lvdatos to 1.98 GB
Logical volume lvdatos successfully resized
shian:~# umount /mnt/datos_lvm/
shian:~# e2fsck -f /dev/vg01/lvdatos
shian:~# resize2fs /dev/vg01/lvdatos
The filesystem on /dev/vg01/lvdatos is now 520192 blocks long.
shian:~# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg01-lvdatos
2.0G 43M 1.9G 3% /mnt/datos_lvm
Y con esto respodo a la duda inicial que me planteó Renato. Espero que te sea útil.