June 2017
Intermediate to advanced
478 pages
13h 14m
English
Content preview from Mastering Embedded Linux Programming - Second Edition
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Discard and TRIM
Usually, when you delete a file, only the modified directory node is written to storage, while the sectors containing the file's contents remain unchanged. When the flash translation layer is in the disk controller, as with managed flash, it does not know that this group of disk sectors no longer contains useful data and so it ends up copying stale data.
In the last few years, the addition of transactions that pass information about deleted sectors down to the disk controller has improved the situation. The SCSI and SATA specifications have a TRIM command and MMC has a similar command named ERASE. In Linux, this feature is known as discard.
To make use of discard, you need a storage device that supports it—most current eMMC ...
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