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Wenn man externe SSDs benutzt sollte man diese aber nicht längere Zeit (~1 Jahr) stromlos/unbenutzt rumstehen lassen. SSDs sind vergesslich und werden mit jedem geschriebenen GB vergesslicher. Da gab es schon böses Erwachen weil manche SSDs für Ihre Backups genommen haben und das dann futsch war. Hin und wieder müssen die angesteckt (und auch mindest einmal komplett ausgelesen werden) damit der Controller die Speicherzellen prüfen und wo notwendig refreshen kann.
Von hier: https://www.crucial.com/support/articles-faq-ssd/ssds-and-smart-data. Das gilt analog für andere Hersteller auch. Im Serverbereich spezifiziert die JEDEC gar nur drei Monate.The lifetime of a NAND-flash device is defined by another characteristic: data retention. Data retention is the amount of time that the device can safely store and allow successful retrieval of user data in an unpowered state. When an SSD or other NAND-flash device is brand new, its unpowered data retention will be several years. However, almost like human memory, it gets shorter as it experiences wear and tear, by writing data (data reads do not directly cause wear).
The Joint Electron Device Engineering Council (JEDEC) is the industry group which creates standards and specifications for semiconductor-based devices and assemblies. Micron is a leading member of JEDEC, which defines data retention in a specific way: For SSDs in client applications (like business or personal computers), data retention for an SSD shall be one year, in an unpowered state, stored at 30 °C (86 °F). This should give most computer users plenty of time to retrieve any data from an unused drive after some time on the shelf, if needed.