[Galaxy S II Q&A, Help & Troubleshooting] valmiera:
C:\adb>adb shell
root@GT-I9100:/ # ls
adb_keys file_contexts property_contexts sideload
boot.txt fstab.smdk4210 res storage
cache init sbin sys
charger init.rc sdcard system
data init.recovery.smdk4210.rc seapp_contexts tmp
default.prop mnt selinux_version ueventd.rc
dev oem sepolicy ueventd.smdk4210.rc
etc proc service_contexts
root@GT-I9100:/ # df
Filesystem 1K-blocks Used Available Use% Mounted on
tmpfs 402468 24 402444 1% /dev
tmpfs 402468 12 402456 1% /tmp
tmpfs 402468 0 402468 0% /storage
127|root@GT-I9100:/ # mount
rootfs on / type rootfs (rw,seclabel)
tmpfs on /dev type tmpfs (rw,seclabel,nosuid,relatime,mode=755)
devpts on /dev/pts type devpts (rw,seclabel,relatime,mode=600)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,seclabel,relatime)
selinuxfs on /sys/fs/selinux type selinuxfs (rw,relatime)
tmpfs on /tmp type tmpfs (rw,seclabel,relatime)
tmpfs on /storage type tmpfs (rw,seclabel,relatime,mode=050,gid=1028)
/dev/block/mmcblk0p9 on /system type ext4 (ro,seclabel,noatime,user_xattr,barrier=1,data=ordered)
root@GT-I9100:/ #

root@GT-I9100:/sdcard # cat /etc/fstab
/dev/block/mmcblk0p9 /system ext4 defaults 0 0
/dev/block/mmcblk0p7 /cache f2fs inline_data,inline_xattr,discard 0 0
/dev/block/mmcblk0p7 /cache ext4 journal_async_commit,errors=panic 0 0
/dev/block/mmcblk0p1 /efs ext4 journal_async_commit,errors=panic 0 0
/dev/block/mmcblk0p10 /data f2fs inline_data,inline_xattr,discard 0 0
/dev/block/mmcblk0p10 /data ext4 noauto_da_alloc,journal_async_commit,errors=panic 0 0
/dev/block/mmcblk0p12 /preload ext4 journal_async_commit 0 0

2|root@GT-I9100:/system # mount -a
mount: '/dev/block/mmcblk0p7'->'/cache': Invalid argument
mount: '/dev/block/mmcblk0p1'->'/efs': No such file or directory
mount: '/dev/block/mmcblk0p10'->'/data': Invalid argument
mount: '/dev/block/mmcblk0p12'->'/preload': No such file or directory

8|root@GT-I9100:/ # umount /dev/block/mmcblk0p10
root@GT-I9100:/ # e2fsck -fv /dev/block/mmcblk0p10
e2fsck 1.42.9 (28-Dec-2013)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information

17784 inodes used (4.52%, out of 393216)
1181 non-contiguous files (6.6%)
21 non-contiguous directories (0.1%)
# of inodes with ind/dind/tind blocks: 7/7/7
Extent depth histogram: 17602/128
635762 blocks used (40.42%, out of 1572864)
0 bad blocks
0 large files

15707 regular files
2022 directories
4 character device files
0 block device files
5 fifos
0 links
34 symbolic links (34 fast symbolic links)
3 sockets
------------
17775 files

root@GT-I9100:/ # cat fstab.smdk4210
# Android fstab file.
#<src> <mnt_point> <type> <mnt_flags and options> <fs_mgr_flags>
# The filesystem that contains the filesystem checker binary (typically /system) cannot
# specify MF_CHECK, and must come before any filesystems that do specify MF_CHECK
# data partition must be located at the bottom for supporting device encryption

/dev/block/mmcblk0p9 /system ext4 ro,noatime wait
/dev/block/mmcblk0p7 /cache f2fs noatime,nosuid,nodev,inline_data,inline_xattr,discard wait
/dev/block/mmcblk0p7 /cache ext4 noatime,nosuid,nodev,journal_async_commit,errors=panic wait,check_spo
/dev/block/mmcblk0p1 /efs ext4 noatime,nosuid,nodev,journal_async_commit,errors=panic wait,check_spo
/dev/block/mmcblk0p10 /data f2fs noatime,nosuid,nodev,inline_data,inline_xattr,discard wait,encryptable=footer,length=-16384
/dev/block/mmcblk0p10 /data ext4 noatime,nosuid,nodev,noauto_da_alloc,journal_async_commit,errors=panic wait,check_spo,encryptable=footer,length=-16384
/dev/block/mmcblk0p12 /preload ext4 noatime,nosuid,nodev,journal_async_commit wait

# vold-managed volumes ("block device" is actually a sysfs devpath)
/devices/platform/dw_mmc/mmc_host/mmc0/mmc0* auto auto defaults wait,voldmanaged=sdcard0:11,noemulatedsd,nonremovable
/devices/platform/s3c-sdhci.2/mmc_host/mmc1* auto auto defaults wait,voldmanaged=sdcard1:auto,encryptable=userdata
/devices/platform/s3c_otghcd/usb* auto auto defaults voldmanaged=usb:auto

# recovery
/dev/block/mmcblk0p5 /boot emmc defaults recoveryonly
/dev/block/mmcblk0p6 /recovery emmc defaults recoveryonly

# zRAM
/dev/block/zram0 none swap defaults zramsize=268435456

This has to be sdcard0. What next? How to mount it manually?

dev_mount command not found in my phone's OS.

# vold-managed volumes ("block device" is actually a sysfs devpath)
/devices/platform/dw_mmc/mmc_host/mmc0/mmc0* auto auto defaults wait,voldmanaged=sdcard0:11,noemulatedsd,nonremovable
/devices/platform/s3c-sdhci.2/mmc_host/mmc1* auto auto defaults wait,voldmanaged=sdcard1:auto,encryptable=userdata