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changeset 5: 4ee259bdc42a
parent: 812feca5a874
child: 4839b0675118
author: Richard Westhaver <ellis@rwest.io>
date: Sun, 16 Jun 2024 22:17:14 -0400
permissions: -rw-r--r--
description: demo-notes 
     1 * NOTE On blocks and devices
     2 :LOGBOOK:
     3 - State "NOTE"       from              [2024-03-02 Sat 21:30]
     4 :END:
     5 [[https://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/dev.html][/dev]]
     6 In Linux, everything is a file.
     7 
     8 /dev/ contains special device files - usually block or character
     9 device.
    10 
    11 major, minor = category, device
    12 0, 5
    13 
    14 mknod - create special device files
    15 
    16 [[https://www.redhat.com/en/blog/linux-block-devices-hints-debugging-and-new-developments][redhat hints]]
    17 
    18 #+begin_src shell
    19   dd if=/dev/zero of=myfile bs=1M count=32
    20   losetup --show -f myfile
    21   ls -al /dev/loop0
    22   losetup -d /dev/loop0 #teardown
    23 #+end_src
    24 
    25 #+begin_src shell
    26   echo "sup dude" > /dev/loop0
    27   dd if=/dev/loop0 -bs=1
    28   dd if=/dev/nvme0 of=/dev/null progress=true
    29   #pacman -S hdparm
    30   hdparm -T /dev/nvme0
    31 #+end_src
    32 
    33 #+begin_src shell
    34 modprobe scsi_debug add_host=5 max_luns=10 num_tgts=2 dev_size_mb=16
    35 #+end_src
    36 
    37 sparsefiles: create with C, dd, or truncate
    38 
    39 #+begin_src shell :results output
    40 truncate --help
    41 #+end_src
    42 
    43 #+RESULTS:
    44 #+begin_example
    45 Usage: truncate OPTION... FILE...
    46 Shrink or extend the size of each FILE to the specified size
    47 
    48 A FILE argument that does not exist is created.
    49 
    50 If a FILE is larger than the specified size, the extra data is lost.
    51 If a FILE is shorter, it is extended and the sparse extended part (hole)
    52 reads as zero bytes.
    53 
    54 Mandatory arguments to long options are mandatory for short options too.
    55   -c, --no-create        do not create any files
    56   -o, --io-blocks        treat SIZE as number of IO blocks instead of bytes
    57   -r, --reference=RFILE  base size on RFILE
    58   -s, --size=SIZE        set or adjust the file size by SIZE bytes
    59       --help        display this help and exit
    60       --version     output version information and exit
    61 
    62 The SIZE argument is an integer and optional unit (example: 10K is 10*1024).
    63 Units are K,M,G,T,P,E,Z,Y,R,Q (powers of 1024) or KB,MB,... (powers of 1000).
    64 Binary prefixes can be used, too: KiB=K, MiB=M, and so on.
    65 
    66 SIZE may also be prefixed by one of the following modifying characters:
    67 '+' extend by, '-' reduce by, '<' at most, '>' at least,
    68 '/' round down to multiple of, '%' round up to multiple of.
    69 
    70 GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
    71 Full documentation <https://www.gnu.org/software/coreutils/truncate>
    72 or available locally via: info '(coreutils) truncate invocation'
    73 #+end_example
    74 
    75 test mkfs.btrfs on 10T dummy block device
    76 #+begin_src shell
    77   dd if=/dev/zero of=/tmp/bb1 bs=1 count=1 seek=10T
    78   du -sh /tmp/bb1
    79   losetup --show -f /tmp/bb1
    80   mkfs.btrfs /dev/loop0
    81 #+end_src
    82 
    83 diagnostics
    84 #+begin_src shell
    85   iostat # pacman -S sysstat
    86   blktrace # paru -S blktrace
    87   iotop # pacman -S iotop
    88 #+end_src
    89 
    90 bcc/ trace: Who/which process is executing specific functions against
    91 block devices?
    92 
    93 bcc/biosnoop: Which process is accessing the block device, how many
    94 bytes are accessed, which latency for answering the requests?
    95 
    96 at the kernel level besides BPF we got kmods and DKMS,
    97 
    98 compression/de-duplication can be done via VDO kernel mod
    99 
   100 https://en.wikipedia.org/wiki/Dynamic_Kernel_Module_Support
   101 
   102 * NOTE save-lisp-and-respawn
   103 :LOGBOOK:
   104 - State "NOTE"       from              [2024-03-02 Sat 22:57]
   105 :END:
   106 #+begin_src lisp
   107   sb-ext:*save-hooks*
   108 #+end_src
   109 
   110 * NOTE syslog for log
   111 :LOGBOOK:
   112 - State "NOTE"       from              [2024-03-03 Sun 16:35]
   113 :END:
   114 sb-posix:
   115 - openlog syslog closelog
   116 - levels: emerg alert crit err warning notice info debug
   117 - setlogmask