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Ubuntu Data Storage Linux

Ubuntu Wants To Enable SSD TRIM By Default 135

Posted by Soulskill
from the getting-into-fighting-trim dept.
jones_supa writes "During the first day of the latest virtual Ubuntu Developer Summit, Canonical developers finally plotted out the enabling of TRIM/DISCARD support by default for solid-state drives on Ubuntu 14.04. Ubuntu developers aren't looking to enable discard at the file-system level since it can slow down delete operations, so instead they're wanting to have their own cron job that routinely runs fstrim for TRIMing the system. In the past there has been talk about the TRIM implementation being unoptimized in the kernel. Around when Linux 3.0 was released, OpenSUSE noted that the kernel performs TRIM to a single range, instead of vectorized list of TRIM ranges, which is what the specification calls for. In some scenarios this results in lowered performance."
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Ubuntu Wants To Enable SSD TRIM By Default

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  • by dreamchaser (49529) on Tuesday November 19, 2013 @07:40PM (#45468413) Homepage Journal

    More like Linux doesn't follow the best practice recommendations of the standard when it wouldn't be all that hard to do so.

  • by Anonymous Coward on Tuesday November 19, 2013 @07:48PM (#45468487)

    A filesystem just notes which blocks are erased, it doesn't actually erase them. A flash based disk would normally keep maintaining the contents of erased blocks, since it doesn't know which blocks are still in use and which are not. Due to the way flash memory based disks work, keeping the contents of erased blocks causes significant overhead. Flash memory is erased and written in big blocks, so to write just a small sector, an SSD has to read a big block, modify it and write it back. This read-modify-write cycle causes so-called write-amplification, where writing a small amount of data actually causes much more data to be (read, erased and then) written to the flash memory. This is the reason why some disks are fast initially but become much slower once the entire capacity has been used once. With TRIM, the OS can tell the disk which blocks are no longer needed, so that the disk can treat them like empty blocks and not copy them in the read-modify-write cycle. (It's actually more complicated, but that's the idea.) The criticism is that the Linux kernel uses TRIM inefficiently (it uses many individual calls instead of combining several discontiguous erased blocks into one TRIM call.)

  • I imagine that discussing the suggestions on Slashdot first is a way to avoid presenting half-baked suggestions to busy developers.

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