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Fstrim, Lvm and Dmcrypt Blog Projects About me Contact Tweet synaptic fault mind dumped How to properly activate TRIM for your SSD on Linux: fstrim, lvm and dm­crypt Language Posted on Saturday, 23rd February 2013 27 comments English Español Unlike hard disk drives (HDDs), NAND flash memory that make SSD cannot overwrite existing data. This means that you first have to delete the old data before writing new one. Flash memory is divided into blocks, which is further divided in pages. The minimum write unit is a page, but the smallest erase unit is a Tags block. apache Applet debian email fpga game Git GNOME hack hardware kernel linux meego networking packages performance power management procmail python RFKill Security ssd tor trim usb virtualization war webkit wireless Categories http://planet.igalia.com http://planet.webkit.org http://planet.webkitgtk.org http://planetsecurity.org Share it! Data can be written directly into an empty page, but only whole blocks can be erased. Therefore, to reclaim the space taken up by invalid data, all the valid data from one block must be first copied and written into the empty pages of a new block. Only then can the invalid data in the original block be erased, making it ready Recent Posts for new valid data to be written. WebKitGTK+ Performance Bot! Do you see the problem? This means that as time goes on, the SSD will internally fragment the blocks How to connect to .onion Tor domains with among the different pages, until that it reaches a point where there won’t be available any empty page. Firefox on Linux Then every time the drive needs to write a block into any of the semi­full pages, it first needs to copy the How to properly activate TRIM for your SSD on current blocks from the page to a buffer, then it has to delete the whole page to finally rewrite the old blocks along with the new one. This means that as time goes on the SSD performance degrades more and more, Linux: fstrim, lvm and dm­crypt because for every write it has to go through a cycle of read­erase­modify­write. This is known as “write Git: Copy a file or directory from another amplification”. repository preserving the history IKEA Hackers: LackRack Without TRIM the disk is unable to know which blocks are in use by a file or which ones are marked as free Unlocking a LUKS encrypted root partition space. This is because when a file is deleted, the only thing the OS does is to mark the blocks that were remotely via SSH used by the file as free inside the file system index. But the OS won’t tell the disk about this. This means OpenRISC: Making the stack 100% free that over time the performance of the SSD disk will degrade more and more, and it don’t matters how much Don’t eject your USB storage: stop it! space you free, because the SSD won’t know about it. RFKill Applet for GNOME What is TRIM? TRIM was invented for solving this problem. TRIM is the name of a command that the Auth External: the Swiss Army Knife of Apache operating system can send to tell the SSD which blocks are free in the filesystem. Auth The SSD uses this information to internally defragment the blocks and keep free pages available to be written quickly and efficiently. Tweets How to active TRIM on Linux? The first thing to know is that TRIM should be enabled on all I/O abstraction RT @News_Executive: Update: layers. This means that if you have an ext4 partition on top of LVM, which in turn is on top of an encrypted Spectacular Photo of the new eruption volume with LUKS/dm­crypt, then you must enable support for TRIM in these three layers: The filesystem, now of #VolcanCalbuco in #Chile LVM and dm­crypt. There is no point in enabling it at the filesystem level if you don’t enable it also on the http://t.co/JcXBQ9lybC other layers. The TRIM command should be translated from one layer to another until reaching the SSD. 1 month ago RT @aszy: Improving Compiler Optimizations Using Machine Learning http://t.co/jfVOO1kfSG 1 month ago Microsoft is going to celebrate the next Debian release!. Not a joke: http://t.co/1NO3dZCjaR @debian 1 month ago RT @r_netsec: Practical Attacks on DOCSIS [PDF] ­ http://t.co/jzYjnytQZa 1 month ago RT @GSICKMINDS: This year to the #gsickminds2015 we have adopted our friends @jsconf code of conduct http://t.co/52U2KdAngu 2 months ago 1. Enabling TRIM support on dm­crypt We simply have to add the option discard inside our crypttab $ cat /etc/crypttab # <target name> <source device> <key file> <options> sda2_crypt /dev/sda2 none luks,discard Note: The usage of TRIM on dm­crypt could cause some security issues like the revelation of which sectors of your disk are unused. 2. Enabling TRIM support on LVM We have to enable the option issue_discards in the LVM configuration. $ cat /etc/lvm/lvm.conf # [...] devices { # [...] issue_discards = 1 # [...] } # [...] 3. Enabling TRIM support on the file system This is the most interesting part. Most people simply add the option “discard” in the mounting options at /etc/fstab. However, this means that every time you delete a file, the OS will be reporting in real­time to the SSD which blocks were occupied by that file and are not longer in use, and then the SSD will have to perform a defragmentation and deletion of those internal blocks, operation which will take an amount of time higher than desired. In order to optimize the performance of the SSD, I strongly advise you to avoid doing the TRIM operation in real time (whenever a file is deleted) because you would be putting an unnecessary extra amount of work over the SSD. In other words: You should not enable the discard option in fstab. Instead, what I recommend is to run a script periodically to tell the SSD which blocks are free with the command fstrim. Doing this operation daily or weekly is more than enough. This way we do not lose any performance due to TRIM when deleting files and we periodically keep informed the SSD about the free blocks. Other advantages of the fstrim way are: If you didn’t enabled correctly the TRIM support in the above layers of your setup, you will receive an error when executing fstrim. On the other hand, if you were using the discard option at fstab you wouldn’t have received any error and you would end thinking that you managed to get TRIM working properly when you didn’t. If you delete a file by mistake (you know it happens), you can recover it before anacron runs your script fstrim. On the other hand, if you were using the discard­at­fstab option you wouldn’t have any chance of recovering the file, because the OS would have told the SSD to TRIM that blocks as soon as you deleted the file, and consequently the SSD has irreversibly destroyed such blocks. Here you have simple script to run fstrim on the /, /boot and /home partitions, which can be programmed to be executed periodically by anacron $ cat /etc/cron.weekly/dofstrim #! /bin/sh for mount in / /boot /home; do fstrim $mount done It’s worth mentioning that both fstrim and discard­at­fstab options only work on filesystems that implement the ioctl FITRIM. Today, such filesystems are: ~/kernel/linux (v3.8) $ grep ­lr FITRIM fs/ | cut ­d/ ­f2 | sort | uniq | xargs echo btrfs ext3 ext4 gfs2 jfs ocfs2 xfs Note: On most setups you will have to rebuild your initramfs with update­initramfs ­u (Debian and derivatives) or dracut ­f (Redhat and derivatives) and reboot the machine after touching the configuration options of LVM or dm­crypt. Update 25­Feb­2013: Seems that Fedora users with a dm­crypt volume will be affected by this problem: https://bugzilla.redhat.com/890533 Update 14­Aug­2014: The following script can be used to automatically detect and fstrim all filesystems that have TRIM support enabled. # To find which FS support trim, we check that DISC­MAX (discard max bytes) # is great than zero. Check discard_max_bytes documentation at # https://www.kernel.org/doc/Documentation/block/queue­sysfs.txt for fs in $(lsblk ­o MOUNTPOINT,DISC­MAX,FSTYPE | grep ­E '^/.* [1­9]+.* ' | awk '{print $1}'); do linux, ssd, trim ← Git: Copy a file or directory from another repository How to connect to .onion Tor domains with Firefox on preserving the history Linux → Leave a comment ? 27 Comments. charlie Friday, 12th April 2013 at 15:50 UTC Reply the default install with encryption sets /boot as ext2. and i guess that doesn’t support Trim. what will the ramifications be to leave /boot as ext2 and not be able to Trim? Reply clopez Friday, 12th April 2013 at 19:14 UTC /boot is usually a very small partition (<500MB usually). So I think is not a big deal to have this without trim support. If you are worried by this, you can change the default to use ext3 for /boot Reply Flaburgan Thursday, 31st October 2013 at 7:04 UTC What about the swap partition? Should I run fstrim on it too? charlie Friday, 12th April 2013 at 21:37 UTC Reply thank you! excellent blog you have! Exon Thursday, 9th May 2013 at 15:30 UTC Reply Thanks for your great information. I used to add discard in fstab before. When I switched to LVM, I needed to implement another way to set the Trim in my SSD.
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