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Both hdparm and mdtrim find free blocks by allocating a large file on the filesystem and resolving what physical location it was assigned to. Regardless of operating system, the drive can detect when the computer writes all zeros to a block, and de-allocate (trim) that block instead of recording the block of zeros.
A solid-state drive (SSD) provides secondary storage for relatively complex systems including personal computers, embedded systems, portable devices, large servers and network-attached storage (NAS). To satisfy such a wide range of uses, SSDs are produced with various features, capacities, interfaces and physical sizes and layouts. [4]
Defragmentation should be disabled on solid-state drives because the location of the file components on an SSD does not significantly impact its performance, but moving the files to make them contiguous using the Windows Defrag routine will cause unnecessary write wear on the limited number of write cycles on the SSD.
The SSD controller will use free blocks on the SSD for garbage collection and wear leveling. The portion of the user capacity which is free from user data (either already TRIMed or never written in the first place) will look the same as over-provisioning space (until the user saves new data to the SSD).
A block, a contiguous number of bytes, is the minimum unit of storage that is read from and written to a disk by a disk driver.The earliest disk drives had fixed block sizes (e.g. the IBM 350 disk storage unit (of the late 1950s) block size was 100 six-bit characters) but starting with the 1301 [8] IBM marketed subsystems that featured variable block sizes: a particular track could have blocks ...
Adding a new block somewhere else and indicating that F has a second extent; Moving files in the way of the expansion elsewhere, to allow F to remain contiguous; Moving file F so it can be one contiguous file of the new, larger size; The second option is probably impractical for performance reasons, as is the third when the file is very large.
The number of defective blocks in different chips within a NAND flash memory varies: a given chip could have all its data blocks worn out while another chip in the same device could have all its blocks still active. Global wear leveling addresses this problem by managing all blocks from all chips in the flash memory together―in a single pool.
With Open Channel SSDs the L2P table is stored in host memory and the host CPU maintains that table. While the Open Channel SSD approach is more flexible, a significant amount of host memory and host CPU cycles is required for L2P management. With an average write size of 4 KB, almost 3 GB RAM is required for an SSD with a size of 1 TB. [9]