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changeset 12: 7d3ccfc2f7a0
parent: 4839b0675118
child: a04ca5a66178
author: Richard Westhaver <ellis@rwest.io>
date: Fri, 16 Aug 2024 23:51:35 -0400
permissions: -rw-r--r--
description: keys 
     1 * NOTE On blocks and devices
     2 :PROPERTIES:
     3 :ID:       c8304ae3-415d-4ccf-8f4c-1f3f6a555e5b
     4 :END:
     5 :LOGBOOK:
     6 - State "NOTE"       from              [2024-03-02 Sat 21:30]
     7 :END:
     8 [[https://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/dev.html][/dev]]
     9 In Linux, everything is a file.
    10 
    11 /dev/ contains special device files - usually block or character
    12 device.
    13 
    14 major, minor = category, device
    15 0, 5
    16 
    17 mknod - create special device files
    18 
    19 [[https://www.redhat.com/en/blog/linux-block-devices-hints-debugging-and-new-developments][redhat hints]]
    20 
    21 #+begin_src shell
    22   dd if=/dev/zero of=myfile bs=1M count=32
    23   losetup --show -f myfile
    24   ls -al /dev/loop0
    25   losetup -d /dev/loop0 #teardown
    26 #+end_src
    27 
    28 #+begin_src shell
    29   echo "sup dude" > /dev/loop0
    30   dd if=/dev/loop0 -bs=1
    31   dd if=/dev/nvme0 of=/dev/null progress=true
    32   #pacman -S hdparm
    33   hdparm -T /dev/nvme0
    34 #+end_src
    35 
    36 #+begin_src shell
    37 modprobe scsi_debug add_host=5 max_luns=10 num_tgts=2 dev_size_mb=16
    38 #+end_src
    39 
    40 sparsefiles: create with C, dd, or truncate
    41 
    42 #+begin_src shell :results output
    43 truncate --help
    44 #+end_src
    45 
    46 #+RESULTS:
    47 #+begin_example
    48 Usage: truncate OPTION... FILE...
    49 Shrink or extend the size of each FILE to the specified size
    50 
    51 A FILE argument that does not exist is created.
    52 
    53 If a FILE is larger than the specified size, the extra data is lost.
    54 If a FILE is shorter, it is extended and the sparse extended part (hole)
    55 reads as zero bytes.
    56 
    57 Mandatory arguments to long options are mandatory for short options too.
    58   -c, --no-create        do not create any files
    59   -o, --io-blocks        treat SIZE as number of IO blocks instead of bytes
    60   -r, --reference=RFILE  base size on RFILE
    61   -s, --size=SIZE        set or adjust the file size by SIZE bytes
    62       --help        display this help and exit
    63       --version     output version information and exit
    64 
    65 The SIZE argument is an integer and optional unit (example: 10K is 10*1024).
    66 Units are K,M,G,T,P,E,Z,Y,R,Q (powers of 1024) or KB,MB,... (powers of 1000).
    67 Binary prefixes can be used, too: KiB=K, MiB=M, and so on.
    68 
    69 SIZE may also be prefixed by one of the following modifying characters:
    70 '+' extend by, '-' reduce by, '<' at most, '>' at least,
    71 '/' round down to multiple of, '%' round up to multiple of.
    72 
    73 GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
    74 Full documentation <https://www.gnu.org/software/coreutils/truncate>
    75 or available locally via: info '(coreutils) truncate invocation'
    76 #+end_example
    77 
    78 test mkfs.btrfs on 10T dummy block device
    79 #+begin_src shell
    80   dd if=/dev/zero of=/tmp/bb1 bs=1 count=1 seek=10T
    81   du -sh /tmp/bb1
    82   losetup --show -f /tmp/bb1
    83   mkfs.btrfs /dev/loop0
    84 #+end_src
    85 
    86 diagnostics
    87 #+begin_src shell
    88   iostat # pacman -S sysstat
    89   blktrace # paru -S blktrace
    90   iotop # pacman -S iotop
    91 #+end_src
    92 
    93 bcc/ trace: Who/which process is executing specific functions against
    94 block devices?
    95 
    96 bcc/biosnoop: Which process is accessing the block device, how many
    97 bytes are accessed, which latency for answering the requests?
    98 
    99 at the kernel level besides BPF we got kmods and DKMS,
   100 
   101 compression/de-duplication can be done via VDO kernel mod
   102 
   103 https://en.wikipedia.org/wiki/Dynamic_Kernel_Module_Support
   104 
   105 * NOTE save-lisp-and-respawn
   106 :PROPERTIES:
   107 :ID:       e58a96e7-7b88-4e4a-b958-3000603d8baa
   108 :END:
   109 :LOGBOOK:
   110 - State "NOTE"       from              [2024-03-02 Sat 22:57]
   111 :END:
   112 #+begin_src lisp
   113   sb-ext:*save-hooks*
   114 #+end_src
   115 
   116 * NOTE syslog for log
   117 :PROPERTIES:
   118 :ID:       2efa5e4a-f063-49bb-9e61-6917eb115c1a
   119 :END:
   120 :LOGBOOK:
   121 - State "NOTE"       from              [2024-03-03 Sun 16:35]
   122 :END:
   123 sb-posix:
   124 - openlog syslog closelog
   125 - levels: emerg alert crit err warning notice info debug
   126 - setlogmask