I have succeeded to transfer everything from a Time Machine backup, but when I wanted to enable the trim by sudo trimforce enable, then after a restart computer just shows the "crossed out circle". To prevent this, Active Garbage collection goes through the disk and moves each page of valid data to a page in another block so the block with invalid data, which has been identified with Trim, can be cleaned out.I am using 2009 macbook pro and I wanted to upgrade the default hdd to a Samsung Evo 850. If the drive were to not go through this process of moving valid information so that invalid information can be deleted, and instead, just keep writing new information to new pages, eventually it would fill up with data, some of it no longer valid. For example, if there are four pages with data in an otherwise empty block and three pages of data are deleted, the remaining page of data must be written to a new block, then all four pages in the old block can be deleted, freeing them up to be rewritten in the future. The problem is that a larger unit of the memory, a block, must be erased before a smaller unit, a page, can be written. Instead, solid state drives need to erase the now invalid data. The Trim command tells the SSD which cells can be erased during idle time, which also allows the drive to organize the remaining data-filled cells and the empty cells to write to to avoid unnecessary erasing and rewriting.įlash memory, which is what SSDs are made of, cannot overwrite existing data the way a hard disk drive can. For optimum life, each cell should be utilized at roughly the same rate as other cells. If data is written and erased from the same NAND cells all the time, those cells will lose integrity.
Trim also affects the longevity of the solid state drive. This takes slightly more time to do than just writing the new information, so using Trim and Active Garbage Collection helps your SSD perform write commands more quickly. The drive would need to erase the existing information, then write the new information. If the Trim command did not exist (as was the case before Windows® 7), then the solid state drive would not know that certain sectors in the drive contained invalid information until the computer told the drive to write new information to that location. The next time the computer is idle, Active Garbage Collection will delete the data. The Trim command tells the drive that the data can be removed. Instead, the area of the SSD that contains the data is marked as no longer used.
Because of the way solid state drives read and write information, the data is not deleted from the drive at the user's command. From the user's perspective, this data has been deleted from a document. The Trim command tells the SSD that specific areas contain data that is no longer in use.
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