[Q] How best to use Android's internal partitions efficiently and leverage SD space? - Android Q&A, Help & Troubleshooting

I see various options for converting system apps <==> user apps and moving or linking some to SD. But I don't see a good general discussion of this. Also, I think my old phone needs a more hard core approach--probably one that trims down /system and reduces how much /system overlaps redundantly with updates on /data. So here goes...
First off, these solutions seem inadequate:
built-in apps2sd: it still fills up internal memory a lot.
s2e: an all-or-nothing approach for each category
free version of link2sd: cannot move-and-link app data, nor system apps
I've been fairly happy with link2sd, but it's still not radical enough for me. Can s2e be combined with it to reclaim even more space?
Assumptions about a stronger solution:
It will require root access.
It will break OTA (can this be turned off safely? can someone link to a good overview of problems/workarounds?)
It *might* require a fairly fast SD card (but still limited to an old phone's bus speeds, etc.) Note: I just bought a 32GB class 10 SDHC card (UHS-1 U3) for my s5360.
It might require one or two paid apps (hopefully not)
One of the most promising options I've seen is to convert system apps to user apps and then move-and-link them to SD. For the conversion step, do the following all do the same thing?
link2sd Plus (paid)
Titanium Backup Pro (paid)
System Tuner (paid) -- I've tried the free ones and move (and freeze) always fails.
app mover (free) http://forum.xda-developers.com/showthread.php?t=1999346
And are there rules of thumb for what can be safely converted?
EDIT: I just found this handy list--my guess is that any green or yellow Yes can be safely converted to a user app and even moved/linked to SD, but that red shouldn't, and think twice before uninstalling yellow :
http://wiki.cyanogenmod.org/w/Barebones#CM-10.1_App_list_.28WIP.29
Can apps that were moved to /data still be updated? I'd especially like to target outdated system apps that are have already been updated anyway and are thus running from /data anyway. My understanding is that 'moving' those to /data doesn't increase /data usage and doesn't reduce performance--just slightly reduces permissions--as long as I don't move/link them to SD.
lightningdude said:
In all seriousness, though, I'm not entirely sure the Link2SD has good implementation of this method. You might try Titanium Backup to convert system to user apps, then try linking it with Link2SD. It may still not work, but it'd be worth a shot, I suppose.
Furthermore, I always delete bloatware I'm not going to use with Titantium Backup. If I need to go back to stock for an OTA, I just flash the complete stock of whatever phone I'm on.
Click to expand...
Click to collapse
If this can all be done successfully, can the internal partitions then be resized? That is, if we safely shunt some of /system and /cache off to SD, can we then let /data steal some space from both? (My s5360 has this by default: /system 230MB, /cache 40MB, /data 197MB)
My old s5360 seems to get full almost immediately after flashing a cm11 rom (LolliKat) and minimal gapps onto it, although I plan to try again with a version of minimal gapps that installs to SD.
For that matter, can some ROMs be installed primarily to SD? I get the impression that that's how some dual-boot (multiROM) approaches work, but I don't really know.
I've also seen one guide for permanently mounting /system as read-write. I think I'd be ok with that (are the security concerns truly awful?), especially if it meant that system apps would update themselves in-place without impacting /data. But I'm guessing it's not that simple.

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can't create /system/... Read-only file system
I found another cool feature of link2sd to "integrate update into system", removing it from data and eliminating the double use of space. The free version includes this feature, but unfortunately it always errors out for me:
`sh: [51]: can't create /system/app/Music.apk.t: Read-only file system`
I tried upgrading to link2sd Plus, since that's the version that includes a convert feature, which requires write access to /system:
C-Jon said:
One of the most promising options I've seen is to convert system apps to user apps and then move-and-link them to SD.
Click to expand...
Click to collapse
But that feature failed too, for the same reason. So I tried all of the following--granting each app superuser access for 10 minutes each time--and they also failed to successfully mount /system as RW:
X-plore - long press the / folder and choose System Shell, then enter `su` and `mount -o remount,rw /system /system`. It gives no error, but if I then immediately `cd system` and try to `mkdir xxzz` it gives an error: `can't create directory 'xxzz' : Read-only file system`. If I use the GUI, I can apparently create a folder under /system with no error, but if I browse up and come back, the folder is gone.
ES File Explorer (free version) - menu, Root Explorer, Mount R/W. I tried running it multiple times, setting both `/` and `/system` to RW. After doing this a couple times, `/` showed up as already RW, but `system` never did. I immediately retried link2sd Integrate--fails with same error.
mountsystemrorw - this app is dedicated to this one task, and when I click "MOUNT /system RW" it claims success ("Your system is now mounted RW!"); but it actually fails. (At least, link2sd Integrate and X-plore still give the same error/failures.)
AnExplorer - menu, Root. I don't see 'mount' options.
Has KitKat made it nearly impossible to mess with /system, even as root? Or am I doing something wrong?
Just in case, I tried re-running "recreate mount scripts" in link2sd, which had worked before, and this time it failed too! `can't create /system/etc/init.d/11link2sd: Read-only file system`. So maybe something has changed since I first installed link2sd. Hmm. I do see this in a thread on stack exchange, "Write access to the system partition is usually blocked by the kernel at boot." But "recreate mount scripts" worked before, *after* I'd flashed the current kernel (Kernel Bangprovn#1.zip) and ROM (LolliKat Stable 2.zip). That's how I got the ext4 partition working for link2sd in the first place.
I'm getting frustrated and don't want to have a big fight every time I want to integrate or convert an app. So I'm wondering just how feasible the following might be...
I've also seen one guide for permanently mounting /system as read-write. I think I'd be ok with that (are the security concerns truly awful?), especially if it meant that system apps would update themselves in-place without impacting /data.
Click to expand...
Click to collapse
I'm guessing they wouldn't simply self-update. But if I could easily run the Integrate step without this RW battle, that might be enough.
If it helps, here is my mount info:
Code:
cat /proc/mounts
rootfs / rootfs ro,noatime,nodiratime 0 0
tmpfs /dev tmpfs rw,seclabel,nosuid,relatime,mode=755 0 0
devpts /dev/pts devpts rw,seclabel,relatime,mode=600 0 0
proc /proc proc rw,noatime,nodiratime 0 0
sysfs /sys sysfs rw,seclabel,noatime,nodiratime 0 0
selinuxfs /sys/fs/selinux selinuxfs rw,noatime,nodiratime 0 0
/sys/kernel/debug /sys/kernel/debug debugfs rw,noatime,nodiratime 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
none /sys/fs/cgroup tmpfs rw,seclabel,relatime,mode=750,gid=1000 0 0
none /sys/fs/cgroup/memory cgroup rw,relatime,memory 0 0
tmpfs /mnt/asec tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
tmpfs /mnt/fuse tmpfs rw,seclabel,relatime,mode=775,gid=1000 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/dev/block/mtdblock8 /system yaffs2 ro,seclabel,noatime,nodiratime 0 0
/dev/block/mtdblock9 /cache yaffs2 rw,seclabel,nosuid,nodev,noatime,nodiratime 0 0
/dev/block/mtdblock10 /data yaffs2 rw,seclabel,nosuid,nodev,noatime,nodiratime 0 0
/dev/block/mmcblk0p2 /data/sdext2 ext4 rw,seclabel,relatime,barrier=1,data=writeback 0 0
/dev/block/vold/179:1 /mnt/media_rw/sdcard0 vfat rw,dirsync,nosuid,nodev,noexec,noatime,nodiratime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/vold/179:1 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,noatime,nodiratime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/fuse /storage/sdcard0 fuse rw,nosuid,nodev,noatime,nodiratime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0

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using bin/mount rather than xbin/mount
I finally found a solution: remount by explicitly using `/system/bin/mount -o ...` rather than just `mount -o ...`. I'm guessing that at some point the version in /system/xbin started taking priority and for some reason that version fails silently. More info here:
http://android.stackexchange.com/a/110883/109855