By moving erasing out of the write process, writes can be faster. The TRIM command allows the operating system to notify the solid state drive (SSD) which data in a particular set of pages can be overwritten, allowing the solid state drive’s controller to manage the erase process between the time when the host initiates a delete and the next write. When a new file is written, individual pages marked for deletion are grouped into a block so they can be erased first, making room for the next write. When data is deleted from flash media, the associated pages on the solid-state drive are flagged for deletion, but not erased - because only blocks can be erased. Data can be read and written at the page level but can only be erased at the block level. NAND flash memory organizes data into pages, and pages are grouped together in blocks. TRIM, which conceptually can be compared to a defrag utility on a spinning hard drive, improves performance by pro-actively freeing up space. TRIM (also spelled trim) is a specific command in a serial ATA (SATA) interface that tells an underlying NAND flash solid state storage device which data it can erase. So, at this point, many but not all major operating systems support TRIM, which is currently available for SATA interfaces only. Android for mobile devices just started to support TRIM in 2013. OpenSolaris began supporting TRIM in the middle of 2010. Microsoft Windows started to support TRIM in late 2009 with Windows Server 2008. Linux started supporting TRIM back in late 2008, but not all file systems supported by Linux support TRIM. TRIM allows a NAND flash device's controller to manage the erase process after data is deleted from a cell and before the next write to that cell occurs. Many operating systems now offer TRIM support, which is designed to improve write performance. The following file systems support TRIM: NTFS, HFS+, EXT4, Btrfs. I was working from the more-or-less official git repo, but what I like about the service Tom linked to is that you can more easily switch between different versions of a file to compare. I do like the alternate links offered below in Tom Yan's comment. This, of course, ought to work as a brute-force fstrim alternative for any filesystem implementation that is able to do discard but not FITRIM. Once you've filled all free space, get rid of the temporary files, letting all the freed blocks be discarded.(For this step to work, you need kernel 4.5 or later, where FAT has fallocate support.) For FAT32 a file is limited to just under 4 GiB, so that's why you may need a bunch of temporary files to use up all the free space. Blow those up to the maximum possible size using fallocate -n (which allocates the blocks without writing anything to them, so will not put much extra wear on the SSD).Mount the filesystem (be sure to use -o discard).While I haven't had a chance to try it yet, I think this might work: So, of course, you'd like the ones considered free by the filesystem to be trimmed.īut there may be hope. That's sort of too bad, because there's at least one perfectly common scenario where you would want a way to TRIM all the existing free blocks at once: you've given your ancient Banana 6000 a nice upgrade by dd-ing the full disk image from the old spinning drive to a shiny new SSD, so now, as far as the SSD is concerned, all of those blocks have been written, whether they matter to the filesystem or not. Several other filesystems have implemented it, but no one seems to have bothered for FAT. Since 2.6.33, you can control whether it does or not.Īs for the FITRIM ioctl, well, that became a thing in 2.6.37, but I do not see any sign that the FAT filesystem code supports it, even in the latest, greatest (as of today) 4.13rc5. From 2.6.28 through 2.6.32, FAT just was written to discard unconditionally. That even predates the mount option, which didn't appear until 2.6.33. It can support the FITRIM ioctl, which is what the userland fstrim command uses to trim all currently-free blocks in bulk when requestedĪ given filesystem implementation can support one, or the other, or both (or none).Īs it turns out, the FAT implementation has been able to do discard since kernel 2.6.28. It can support the -o discard mount option, so blocks that become free are trimmed immediately There are two different ways a Linux filesystem implementation can "support" TRIM: but it comes up early in searches on the topic, so it seemed to be worth giving an answer from the kernel sources.
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