Differences

This shows you the differences between two versions of the page.

--- software:files [2024/04/04 22:21]
cyril
+++ software:files [2024/04/22 00:04] (current)
cyril [Tools]
@@ Line 23: / Line 23: @@
 === Partitions ===
-  * If you want to use LVM and don't need to boot on the disk, nothing to do in this section, skip to the next one to create the LVM volumes directly on the raw device.
+  * If you want to use LVM and don't need to boot on the disk, not much to do in this section, just remove all the existing partitions with ''gparted'', then go directly to the next one to create the LVM volumes directly on the raw device.
   * Otherwise, create a ''gpt'' partition table with ''gparted''
   * If you need to boot on the disk, create the required ''boot'' and ''grub'' partitions with ''gparted''
@@ Line 31: / Line 31: @@
 === LVM ===
-  * Note that depending on your use case, i.e. whether you want multiple partitions having the same password or not, you may want
   * create physical volume: ''pvcreate <device-name>''.
     * Check with ''pvdisplay'' or ''pvs''.
@@ Line 41: / Line 40: @@
     * ''<absolute-size>'': ''200G'', ''3T'', ...
     * ''<relative-size>'': ''+100%FREE''
+  * If using an SSD drive, [[#ssd_trim|TRIM commands]] from the layers below (eg filesystem) will be transparently forwarded without any special configuration. However if you wish that LVM issues its own TRIM commands when some space is not allocated by LVM, you can set the ''issue_discards'' option to 1 in ''/etc/lvm/lvm.conf''.
 === LUKS ===
@@ Line 49: / Line 50: @@
     * By default it will configure the key derivation take 2 seconds
   * Open (decrypt) the volume: ''cryptsetup luksOpen <volume-name> <evolume-name!>''
+  * If using an SSD drive, you probably should enable [[#ssd_trim|TRIM-forwarding]]: ''cryptsetup --allow-discards --persistent refresh <evolume-name>'' (check [[https://wiki.archlinux.org/title/Solid_state_drive#dm-crypt|security implications]] though)
 === Filesystem ===
@@ Line 124: / Line 126: @@
       * can also be used to change compression of existing files (but breaks deduplication) with option ''-czstd'' (inherits level specified at mount).
     *  ''btrfs filesystem balance -dusage=<percentage>'' for **defragmenting free space** (only data chunks less full than ''<percentage>'' will be compacted).
+  * ''filefrag -v <file>'' to analyze the fragmentation of a file, and list all extents.
+=== Compression ===
+  * With ''btrfs'':
+    * ''compsize <subvolume-path>'' in order to get statistics about quantity of compressed files, and compression ratio.
+    * ''compsize <file-path>'' in order to get compression details about a specific file.
+=== SSD TRIM ===
+  * TRIM (or discard) operation means informing the SSD drive about the unused memory, so that it can perform efficiently wear leveling.
+  * Checking TRIM support: run ''lsblk --discard'', and check for non-zero values in columns DISC-GRAN (DISCard GRANularity) and DISC-MAX (DISCard MAX bytes).
+  * **Warning**: make sure that your device supports TRIM before using it, or data loss can occur.
+  * Each layer must forward the TRIM commands to the layer above, until it reaches the drive. If you haven't done it persistently for LUKS as suggested in the [[#luks|create]] section, you can open it with this option: ''cryptsetup <...> --allow-discards''
+  * Then two options are available to enable it:
+    * Continuous TRIM, i.e. configuring the filesystem to notify instantly each block that is freed.
+      * It is not advised because doing it to often can reduce the lifetime of poor quality SSDs.
+    * Periodic TRIM, i.e. explicitly notifying the free blocks periodically.
+      * Using the ''fstrim'' utils from the util-linux package.
+      * Manually: run ''fstrim --verbose <mount-point>'' for a single volume, or ''fstrim --verbose -A'' for all mounted filesystems listed in ''/etc/fstab'' and the root filesystem inferred from the kernel command line.
+      * Weekly: enable the timer ''systemctl start fstrim.timer''
+Source : https://wiki.archlinux.org/title/Solid_state_drive
 === Resizing ===
@@ Line 145: / Line 171: @@
 === Borg Backup ===
+  * Create a Borg repository in the current folder: <code>borg init -e <encryption> [--append-only] .</code>
+    * ''<encryption>'' can be:
+      * ''none'' to disable it, for instance on an already encrypted volume
+      * ''repokey'' to enable it (or ''repokey-blake2'' to use Blake2 instead of Sha256, which is often faster)
+      * ''authenticated'' to disable encryption but still enable authentication (or ''authenticated-blake2'' to use Blake2)
+    * ''--append-only'' means that no data can be removed with borg, archives can only be added. It can be used to protect an online repository against malware.
+  * Create archives: <code>borg create <repo>::<!archive> <path> --stats --progress
+    --compression auto,zstd,12 --chunker-params 15,23,19,4095 --noctime -x --exclude-caches</code>
+    * ''--compression'': it can make sense to adjust the compression level depending on your computer speed and your storage speed, so that compression does not slow down the backup, but still save as much space as possible under this constraint. However it is not always easy to find an universal value (data that compress very well are mostly limited by the input storage speed, while data that compress less well are mostly limited by the output storage speed). You have roughly the choice between LZ4 (very quick), LZMA (very high compression ratio), and ZSTD (wide-range) in between.
+    * ''--chunker-params'': this is also an important but a bit complicated tuning. Originally default value was creating small chunks causing huge cache and memory usage, so they switched to much larger chunks, but which can be too large for some applications (for instance when modifying only metadata of an image file, we want to deduplicate the data), so I came with this compromise ''15,23,19,4095''.
+  * ''borg info <repo>''
+  * ''borg list <repo>''
+  * ''borg info <repo>::<archive>''
 === Restic ===
+  * Create a Restic repository in the current folder: <code>restic init --repo .</code>
+    * Note that encryption **and** password are mandatory, [[https://github.com/restic/restic/issues/4326|because]]. However you can store the password in a file in the repository, or use the a password file with ''--password-file''.
+  * Create snapshots: <code>restic --repo <repo> --verbose --compression auto --ignore-ctime backup <path></code>
+    * The chunker cannot be configured, contrary to Borg. It is equivalent to [[https://restic.readthedocs.io/en/stable/100_references.html#backups-and-deduplication|19,23]],[[https://restic.net/blog/2015-09-12/restic-foundation1-cdc/|21,512]], similarly to Borg's default [[https://borgbackup.readthedocs.io/en/stable/internals/data-structures.html#buzhash-chunker|19,23,21,4095]], but unlike my chosen values.
+    * ''--compression'': unlike Borg, there is only choicies ''auto'', ''max'' and ''off''
 === BTRFS snapshots ===
@@ Line 159: / Line 205: @@
+===== Container files =====
+Sources:
+  * [[https://serverfault.com/questions/696554/creating-a-grow-on-demand-encrypted-volume-with-luks|Excellent demonstration]] for creating a growing container file with LUKS and EXT4 using sparse files.
 ===== Digital Will =====