Benefits of expandable storage
This article documents the benefits of being able to expand the storage of one's mobile device using memory card.
Many mobile phones allow the user to expand the internal storage, usually using MicroSD-cards. However, since 2015, non-Apple mobile phones with no expandable storage have increasingly been emerging on the market, forcing users to store data on the device's internal storage.
During the 2010s decade, the storage capacity of MicroSD-XC cards has increased exponentially, allowing the earliest phones with MicroSD-XC support such as the 2012 Samsung Galaxy S3 to expand the available storage to hundreds of gigabytes.
Limited internal storage
In comparison to MicroSD cards, internal mobile phone storage has only increased very slowly until the mid-2010s.
Even the 2016 Samsung Galaxy S7 was only available with 32 GB of total[note 1] internal memory, which can fill up quickly with 2160p (6 MB/s used) and 720p@240fps slow motion (9 MB/s used) video recording, offline films, maps and audio books.
Only after then did the internal storage of mobile phones increase significantly, bringing the 2018 Galaxy Note 9 variant with 0.5 terabytes (512 GB) of internal storage only 21⁄2 years later.
Mass storage access
A computer can have direct (low-level/near-hardware) mass storage access to a MicroSD card, if accessed by the computer through an card reader and/or adapter rather than through Media Transfer Protocol (MTP). The latter only provides poor technical control of the storage to the user.
The technical control provided by mass storage access can provide several assuring benefits:
If a mobile phone breaks and becomes unbootable, whether due to drop damage, water damage, malware intrusion, software failure (while updating or defects as a result of bootloader- and root-related actions, known as “bricking”), data stored on the MicroSD card has the highest likelihood of survival.
In case of a defective mobile phone, data stored on the MicroSD card can usually be retrieved with ease, while recovering data from the internal memory of a defective mobile phone usually requires heavy and expensive forensic work.
If a factory reset is necessary due to an inadvertent system failure, all data stored on the internal storage is erased upon reset, where as data stored on the memory card can be salvaged externally.
On earlier phones, users have reported the internal user storage randomly disappearing. Data stored on MicroSD cards would be unaffected and retrievable in that case.
Although MTP (mass storage protocol) sufficient in many cases, and provides the benefit of safe ejections due to its abstraction layer to the computer controlled by the mobile phone's operating system, MTP is outdated early-2000s technology that lacks support for parallelism, which causes unresponsive file transfer and browsing, if done simultaneously. MTP tends to randomly freeze indefinitely, and merely loading the list of hundreds of files may take upwards of a minute.
MicroSD, if accessed directly from a computer, allows bypassing MTP's bugginess and provides the smoooth performance and parallelism of mass-storage.
An alternative to both is running an FTP server from the mobile phone using
com.amaze.filemanager[note 2] and downloading the files from the computer, or vice-versa (upload from phone).
As of 2020, mobile phone operating systems still lack the option to write-protect an MTP connection, while MicroSD cards can be read through a main-size SD card adapter, which has a write protection switch on the side, which provides reliable write protection if obeyed by the SD card reading hardware.
Writing on a MicroSD card instead of the internal storage spares the limited re-writing cycles of the mobile phone's internal NAND flash memory from being worn down, although flash storage usually has sufficient writing cycles to function as long as needed with average use, and especially outlasts non-replaceable batteries.
For heavy usage though, such as hosting a portable FTP server (or FTP hotspot), and heavy camera usage, a MicroSD card better take over the workload and protect the internal storage from weardown.
Upon running out of remaining space storage on the MicroSD card, one can replace the full card with an empty one instead of having to move the data through conventional methods.
As described in Benefits of user-replaceable batteries § Instant swap as a benefit of user-replaceable batteries, it is less valid on devices with memory card compartments that are harder to access, but still much faster than having to clear the mobile phone's internal storage by moving files elsewhere.
This section debunks arguments disclaiming the necessity of expandable storage in mobile phones.
Cloud storage argument
- “Who needs user-expandable storage if there is the cloud?”
Cloud storage and MicroSD cards are fundamentally different and can not fullfill the purpose of each other.
While cloud (or remote FTP) storage is insuring in the unlikely case of a physically lost device, it relies on steadily available, preferably fast Internet connection, which is location-dependent.
Transfer rates and data volumes
Uploading and accessing multimedia content to/from a cloud or private server may be a burden on a mobile data plan, while data stored on a MicroSD card is steadily and unlimitedly available.
Memory cards can be recorded to in real time due to abundant storage speeds, even compared to 2160p (4K) video, which commonly is recorded witha bit rate of 6 MB/s (48 Mbit/s) on mobile phones — a fraction of storage speeds commonly supported by MicroSD cards (>50 MB/s, which is >400 Mbit/s).
As described in Data loss prevention § Clouds are only redundant, cloud storage is not nearly as trustable and reliable as offline storage, and potential technical failures are far less predictable to end users.
A user has no technical control over a cloud storage provider, while memory cards provide a much greater sense of control, ownership, privacy and proximity.
An argument commonly cited by form-over-function advocates for why a lack of MicroSD storage expandability be trifling is that the storage still be “expandable” using a flash drive or MicroSD card reader adapter connected via USB-OTG.
However, for the following reasons, a USB-OTG flash drive or card reader is no valid replacement for expandable storage:
- Blatant bulk
The USB-OTG adapter, both in cabled and cable-less forms, reserves the device's USB charging port while connected, making wired charging impossible whilst being used. In comparison, the MicroSD card is housed inside the device's casing, without directly interfering with any device functionality.
Special adapters which claim to allow simultaneous charging and USB OTG usage may not be compatible with many devices and often restrict charging speeds to dystopian levels such as 1 watt.
Due to being externally attached, a USB-OTG accessory sticks out of the device, diminishing its ergonomy.
Putting the device in the trousers or dropping the device on its bottom while the USB-OTG adapter is connected may wear down the port quickly, leading to a loose contact.
A USB-OTG connector is not nearly as stable as a MicroSD card slot and could also be disconnected accidentally. Writing data during an unstable connection or accidental disconnection could lead to file system corruption.
Many mobile applications have not even been programmed to make direct use of USB-OTG, including precluded system software such as the camera software.
- The bulk paradox
As described in Benefits of user-replaceable batteries § Bulk argument, a marginal reduction of what form-over-function advocates describe as bulk could lead to the dependence to much more actual bulk.
Before 2015, all known Samsung mobile phones were equipped with a MicroSD card slot, while some mobile phones since 2015, starting with the Galaxy S6 lack expandable storage.
However, unlike user-replaceable batteries, many more mobile phones released between 2015 and 2020 are equipped with MicroSD support.
- A few gigabytes of internal storage are reserved for the operating system and precluded software. This margin becomes more critical with less internal storage.
- The former is more functional and supports Android Storage Access Framework, while the latter appears to have a better compatibility to older FTP clients. Both are open-source.
- Gordon, Whitson (2011-10-26). "How Do I Fix My Bricked Android Phone?". Lifehacker.
- Unge, Simon (2020-01-29). "Alles weg". YouTube (video) (in Deutsch). Text " #hochformat " ignored (help) – The iPhone of a German YouTube celebrity, Simon Unge, experienced a system failure where it refused to boot, forcing Simon to do a factory reset. He lost video material and other data in the process. Had the data been stored on a memory card, it could have been salvaged externally instead of being gone.
- XDA-Developers forum thread: Omnia 2 doesn't recognize internal storage! by WhiteRussianBC (2010-09-02)
- Video: Samsung Galaxy Note 9 “Ingenious” commercial series — Part: Expandable storage
- Card versus cloud – Western Digital blog
- Smith, Chris (9 April 2015). "Don't freak out about Galaxy S6's lack of microSD support – here's what you can do about it". BGR.