[Samsung Galaxy Nexus] Lanchon:
first, the google fix, which is not google's but samsung's done under google pressure, has nothing to do with read-only locked emmcs, it is supposed to fix a different issue. from a PM i wrote yesterday:

second, regarding the "the increasing access delay of the EMMC when the partition is nearly full":

this is INHERENT to every flash device in existence. as free space nears zero, write amplification factor tends to infinite. write amplification is the effect that requires that flash memory actually write more under the hood than the volume of user data the user requested to write. healthy values of 1.1 don't create a real impact, but with low free space, factors of 10 or more can happen. this reduces the write performance of the flash to much less than 10% of the original value (much less because erase times are not counted in the WA factor).

basically the system grinds to a halt. not only that, the limited life of the flash (ssd or emmc) is burnt away at a very fast pace due to the amplified write volume. using a flash memory without a minimum of 20% free space is ignorant and brain dead, you just don't!

some setups WILL NOT REVERT from this situation EVER, even if you free the space. only systems that fully support TRIM can; in others, the WA can only ever increase and there is no way to turn back the clock. this is why, especially on older hardware, it is very important to NEVER fill the flash, if only briefly. even then, some file systems will increase the WA even if you never fill them up, and there is nothing you can do.

put plainly, non-TRIM flash systems are defective engineering doomed to ever decreasing performance and early failure.

now what's the issue in this thread?

slow gnex? free >25%, preferibly 33%, of space, ensure android 4.3 or later is in the device, and let the device rest. in 24 to 48 hs it will trim and its speed will recover to acceptable levels. you will find the trim events done in a maintenance window in the log.

locked emmc? no known cure. but i'll look into that firmware upgrade thread on that creepy site later.

---------- Post added at 12:58 PM ---------- Previous post was at 12:31 PM ----------

and a note i want to add:

ALL flash behaves in the same way. but manufacturers never let you use the full size of the flash, a fraction of it is reserved as free space forever, and this limits how high the WA factor can go in a specific device even if you use it ignorantly. this is called overprovisioning in the business. different manufacturers choose different OP factors.

for example, in an SSD with 256 GiB of flash (it is always a power of 2), there are approximately 275,000,000,000 bytes (or 275 GB) of storage. (if you dont know the difference between GiB and GB, google it.) but those SSDs are never marketed as 275 GB devices: you will only find 250 GB and 240 GB models. now from the 275 GB subtract the space for the embedded firmware and for FTL data structures which are device-specific, but still you are left with a figure much higher than 250 GB. where is all this missing space you say? it's overprovisioning.

typical figures in the industry run from 7% on basic consumer to 14% on higher performance models. so now you know why a 250GB ssd is not better than a 240GB device, it's just a marketing gimmick.

but is it worse then? nope. the manufacturer chooses a minimum overprovision, but you can choose your own above that. just partition the SSD so that you leave some unpartitioned space at the end (and make sure that that space is trimmed, as when the device is in a factory new state) and voila, you increased your OP. so less forced OP affords choice.

i dont do this to my devices because i'm a responsible user: if i ever need the space i can use it briefly; i prefer to have that temporary option if i'm ever on a hard place. but for devices i set up for other people (like repartitioned phones) i always do it. one way to do this on the i9100 is to enlarge the system partition by and trim it after installing the system; the enlarged /system is welcome on that device anyway.