[Samsung Galaxy Core.] StratOS_HTC:
EFS

This has to be done like this way :

If's for GC2, on Core i826 it will be similar :

1. find out where EFS is mounted :

You can try it with mount (U'll need SU acess) and then search for efs :

rootfs / rootfs ro,relatime 0 0
tmpfs /dev tmpfs rw,seclabel,nosuid,relatime,mode=755 0 0
devpts /dev/pts devpts rw,seclabel,relatime,mode=600 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,seclabel,relatime 0 0
selinuxfs /sys/fs/selinux selinuxfs rw,relatime 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
none /sys/fs/cgroup tmpfs rw,seclabel,relatime,mode=750,gid=1000 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/secure tmpfs rw,seclabel,relatime,mode=700 0 0
tmpfs /mnt/secure/asec tmpfs rw,seclabel,relatime,mode=700 0 0
/dev/block/vold/179:129 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,noatime,nodiratime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
tmpfs /mnt/asec tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
/dev/block/dm-0 /mnt/asec/nextapp.fx.rk-1 ext4 ro,dirsync,seclabel,nosuid,nodev,noatime,errors=continue 0 0
tmpfs /mnt/obb tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
/dev/block/platform/sprd-sdhci.3/by-name/system /system ext4 ro,seclabel,relatime,errors=panic,data=ordered 0 0
/dev/block/platform/sprd-sdhci.3/by-name/userdata /data ext4 rw,seclabel,nosuid,nodev,noatime,discard,journal_checksum,journal_async_commit,noauto_da_alloc,errors=panic,data=ordered 0 0
/dev/block/platform/sprd-sdhci.3/by-name/CSC /cache ext4 rw,seclabel,nosuid,nodev,noatime,discard,journal_checksum,journal_async_commit,noauto_da_alloc,errors=panic,data=ordered 0 0
[COLOR="Red"][B]/dev/block/platform/sprd-sdhci.3/by-name/efs /efs ext4 rw,seclabel,nosuid,nodev,noatime,discard,journal_checksum,journal_async_commit,noauto_da_alloc,data=ordered 0 0
/data/media /mnt/shell/emulated sdcardfs rw,nosuid,nodev,relatime,uid=1023,gid=1023,derive=legacy,reserved=20MB 0 0[/B][/COLOR]
tmpfs /storage/emulated tmpfs rw,seclabel,nosuid,nodev,relatime,mode=050,gid=1028 0 0
/dev/block/vold/179:129 /mnt/media_rw/extSdCard vfat rw,dirsync,nosuid,nodev,noexec,noatime,nodiratime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/mnt/media_rw/extSdCard /storage/extSdCard sdcardfs rw,nosuid,nodev,relatime,uid=1023,gid=1023,derive=unified 0 0
/data/media /storage/emulated/0 sdcardfs rw,nosuid,nodev,relatime,uid=1023,gid=1023,derive=legacy,reserved=20MB 0 0
/data/media /storage/emulated/0/Android/obb sdcardfs rw,nosuid,nodev,relatime,uid=1023,gid=1023,derive=legacy,reserved=20MB 0 0
/data/media /storage/emulated/legacy sdcardfs rw,nosuid,nodev,relatime,uid=1023,gid=1023,derive=legacy,reserved=20MB 0 0
/data/media /storage/emulated/legacy/Android/obb sdcardfs rw,nosuid,nodev,relatime,uid=1023,gid=1023,derive=legacy,reserved=20MB 0 0

or just plain ls :

ls -l /dev/block/platform/*/by-name/
lrwxrwxrwx root root 2014-11-10 14:25 CSC -> /dev/block/mmcblk0p19
lrwxrwxrwx root root 2014-11-10 14:25 FIXNV1 -> /dev/block/mmcblk0p1
lrwxrwxrwx root root 2014-11-10 14:25 FIXNV2 -> /dev/block/mmcblk0p2
lrwxrwxrwx root root 2014-11-10 14:25 FOTA_SIG -> /dev/block/mmcblk0p9
lrwxrwxrwx root root 2014-11-10 14:25 HIDDEN -> /dev/block/mmcblk0p21
lrwxrwxrwx root root 2014-11-10 14:25 KERNEL -> /dev/block/mmcblk0p17
lrwxrwxrwx root root 2014-11-10 14:25 MODEM -> /dev/block/mmcblk0p7
lrwxrwxrwx root root 2014-11-10 14:25 MODEM_BACKUP -> /dev/block/mmcblk0p8
lrwxrwxrwx root root 2014-11-10 14:25 OTA -> /dev/block/mmcblk0p10
lrwxrwxrwx root root 2014-11-10 14:25 Odin_reserved -> /dev/block/mmcblk0p16
lrwxrwxrwx root root 2014-11-10 14:25 PARAM -> /dev/block/mmcblk0p13
lrwxrwxrwx root root 2014-11-10 14:25 RECOVERY -> /dev/block/mmcblk0p18
lrwxrwxrwx root root 2014-11-10 14:25 RUNTIMENV1 -> /dev/block/mmcblk0p11
lrwxrwxrwx root root 2014-11-10 14:25 RUNTIMENV2 -> /dev/block/mmcblk0p12
lrwxrwxrwx root root 2014-11-10 14:25 SBL1 -> /dev/block/mmcblk0p3
lrwxrwxrwx root root 2014-11-10 14:25 SBL2 -> /dev/block/mmcblk0p4
lrwxrwxrwx root root 2014-11-10 14:25 WDSP -> /dev/block/mmcblk0p5
lrwxrwxrwx root root 2014-11-10 14:25 WDSP_BACKUP -> /dev/block/mmcblk0p6
[B][COLOR="Red"]lrwxrwxrwx root root 2014-11-10 14:25 efs -> /dev/block/mmcblk0p14[/COLOR][/B]
lrwxrwxrwx root root 2014-11-10 14:25 fixnv1 -> /dev/block/platform/sprd-sdhci.3/by-name/FIXNV2
lrwxrwxrwx root root 2014-11-10 14:25 fixnv2 -> /dev/block/platform/sprd-sdhci.3/by-name/FIXNV1
lrwxrwxrwx root root 2014-11-10 14:25 prodnv -> /dev/block/mmcblk0p15
lrwxrwxrwx root root 2014-11-10 14:25 runtimenv1 -> /dev/block/platform/sprd-sdhci.3/by-name/RUNTIMENV1
lrwxrwxrwx root root 2014-11-10 14:25 runtimenv2 -> /dev/block/platform/sprd-sdhci.3/by-name/RUNTIMENV2
lrwxrwxrwx root root 2014-11-10 14:25 system -> /dev/block/mmcblk0p20
lrwxrwxrwx root root 2014-11-10 14:25 userdata -> /dev/block/mmcblk0p22

so now u know it's in /dev/block/platform/sprd-sdhci.3/by-name/efs or it equals /dev/block/mmcblk0p14

ls -l /dev/block/platform/sprd-sdhci.3/by-name/efs
lrwxrwxrwx root root 2015-03-10 22:16 efs -> /dev/block/mmcblk0p14

now just need to copy it to the extSdCard :

root@kanas3gnfc:/ # cat /dev/block/platform/sprd-sdhci.3/by-name/efs>/storage/extSdCard/EFS

or dd:

root@kanas3gnfc:/ # dd if=/dev/block/mmcblk0p14 of=/storage/extSdCard/EFS bs=2048
f=/storage/extSdCard/EFS bs=2048
10240+0 records in
10240+0 records out
20971520 bytes transferred in 0.664 secs (31583614 bytes/sec)

Now you have a backup.

Regards