changelog shortlog graph tags branches changeset files revisions annotate raw help

Mercurial > org > notes / 20240302.org

changeset 2: 04e86b94ef1a
parent: 87b04952fb18
child: 812feca5a874
author: Richard Westhaver <ellis@rwest.io>
date: Thu, 06 Jun 2024 23:16:37 -0400
permissions: -rw-r--r--
description: style update 
     1 #+setupfile: ../clean.theme
     2 * NOTE On blocks and devices
     3 :LOGBOOK:
     4 - State "NOTE"       from              [2024-03-02 Sat 21:30]
     5 :END:
     6 [[https://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/dev.html][/dev]]
     7 In Linux, everything is a file.
     8 
     9 /dev/ contains special device files - usually block or character
    10 device.
    11 
    12 major, minor = category, device
    13 0, 5
    14 
    15 mknod - create special device files
    16 
    17 [[https://www.redhat.com/en/blog/linux-block-devices-hints-debugging-and-new-developments][redhat hints]]
    18 
    19 #+begin_src shell
    20   dd if=/dev/zero of=myfile bs=1M count=32
    21   losetup --show -f myfile
    22   ls -al /dev/loop0
    23   losetup -d /dev/loop0 #teardown
    24 #+end_src
    25 
    26 #+begin_src shell
    27   echo "sup dude" > /dev/loop0
    28   dd if=/dev/loop0 -bs=1
    29   dd if=/dev/nvme0 of=/dev/null progress=true
    30   #pacman -S hdparm
    31   hdparm -T /dev/nvme0
    32 #+end_src
    33 
    34 #+begin_src shell
    35 modprobe scsi_debug add_host=5 max_luns=10 num_tgts=2 dev_size_mb=16
    36 #+end_src
    37 
    38 sparsefiles: create with C, dd, or truncate
    39 
    40 #+begin_src shell :results output
    41 truncate --help
    42 #+end_src
    43 
    44 #+RESULTS:
    45 #+begin_example
    46 Usage: truncate OPTION... FILE...
    47 Shrink or extend the size of each FILE to the specified size
    48 
    49 A FILE argument that does not exist is created.
    50 
    51 If a FILE is larger than the specified size, the extra data is lost.
    52 If a FILE is shorter, it is extended and the sparse extended part (hole)
    53 reads as zero bytes.
    54 
    55 Mandatory arguments to long options are mandatory for short options too.
    56   -c, --no-create        do not create any files
    57   -o, --io-blocks        treat SIZE as number of IO blocks instead of bytes
    58   -r, --reference=RFILE  base size on RFILE
    59   -s, --size=SIZE        set or adjust the file size by SIZE bytes
    60       --help        display this help and exit
    61       --version     output version information and exit
    62 
    63 The SIZE argument is an integer and optional unit (example: 10K is 10*1024).
    64 Units are K,M,G,T,P,E,Z,Y,R,Q (powers of 1024) or KB,MB,... (powers of 1000).
    65 Binary prefixes can be used, too: KiB=K, MiB=M, and so on.
    66 
    67 SIZE may also be prefixed by one of the following modifying characters:
    68 '+' extend by, '-' reduce by, '<' at most, '>' at least,
    69 '/' round down to multiple of, '%' round up to multiple of.
    70 
    71 GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
    72 Full documentation <https://www.gnu.org/software/coreutils/truncate>
    73 or available locally via: info '(coreutils) truncate invocation'
    74 #+end_example
    75 
    76 test mkfs.btrfs on 10T dummy block device
    77 #+begin_src shell
    78   dd if=/dev/zero of=/tmp/bb1 bs=1 count=1 seek=10T
    79   du -sh /tmp/bb1
    80   losetup --show -f /tmp/bb1
    81   mkfs.btrfs /dev/loop0
    82 #+end_src
    83 
    84 diagnostics
    85 #+begin_src shell
    86   iostat # pacman -S sysstat
    87   blktrace # paru -S blktrace
    88   iotop # pacman -S iotop
    89 #+end_src
    90 
    91 bcc/ trace: Who/which process is executing specific functions against
    92 block devices?
    93 
    94 bcc/biosnoop: Which process is accessing the block device, how many
    95 bytes are accessed, which latency for answering the requests?
    96 
    97 at the kernel level besides BPF we got kmods and DKMS,
    98 
    99 compression/de-duplication can be done via VDO kernel mod
   100 
   101 https://en.wikipedia.org/wiki/Dynamic_Kernel_Module_Support
   102 
   103 * NOTE save-lisp-and-respawn
   104 :LOGBOOK:
   105 - State "NOTE"       from              [2024-03-02 Sat 22:57]
   106 :END:
   107 #+begin_src lisp
   108   sb-ext:*save-hooks*
   109 #+end_src
   110 
   111 * NOTE syslog for log
   112 :LOGBOOK:
   113 - State "NOTE"       from              [2024-03-03 Sun 16:35]
   114 :END:
   115 sb-posix:
   116 - openlog syslog closelog
   117 - levels: emerg alert crit err warning notice info debug
   118 - setlogmask