Te pongo el texto, ¿vale?:
"## Vold 2.0 Generic fstab
## - San Mehat ([email protected])
##
#######################
## Regular device mount
##
## Format: dev_mount <label> <mount_point> <part> <sysfs_path1...>
## label - Label for the volume
## mount_point - Where the volume will be mounted
## part - Partition # (1 based), or 'auto' for first usable partition.
## <sysfs_path> - List of sysfs paths to source devices
######################
## Example of a standard sdcard mount for the emulator / Dream
# Mounts the first usable partition of the specified device
#dev_mount sdcard /mnt/sdcard auto /devices/platform/goldfish_mmc.0 /devices/platform/msm_sdcc.2/mmc_host/mmc1
#dev_mount flash /mnt/sdcard auto /devices/virtual/mtd/mtd9/mtdblock9
dev_mount flash /mnt/sdcard auto /dev/block/mtd/by-name/user /dev/block/platform/emmc/by-name/user
dev_mount sdcard /mnt/external_sd auto /devices/platform/rk29_sdmmc.0/mmc_host/mmc
dev_mount udisk /mnt/usb_storage auto /devices/platform/usb20_host/usb /devices/platform/usb20_otg/usb
## Example of a dual card setup
# dev_mount left_sdcard /sdcard1 auto /devices/platform/goldfish_mmc.0 /devices/platform/msm_sdcc.2/mmc_host/mmc1
# dev_mount right_sdcard /sdcard2 auto /devices/platform/goldfish_mmc.1 /devices/platform/msm_sdcc.3/mmc_host/mmc1
## Example of specifying a specific partition for mounts
# dev_mount sdcard /sdcard 2 /devices/platform/goldfish_mmc.0 /devices/platform/msm_sdcc.2/mmc_host/mmc1
"
De lo poco que yo entiendo de esto, las lineas válidas son las que no llevan delante la almohadilla, ¿no?.
Por otro lado, cuando lo cambie, imagino que será sustituir lo que me digas, guardar los cambios, apagar, meter la tarjeta y reiniciar la tablet con la tarjeta dentro. ¿Debería ser así?.