I am trying to measure the speed of reading a given block size using the dd command. However depending on which input I use: a regular file (on the same device) or /dev/sdb1, I get some really different results.
Note:
- Freshly formated ext4
ATA device, with non-removable media
Transport: Serial, SATA Rev 3.0
- I did the same experiment with varying blocksizes, and up to 128K the phenomena is the same.
- The file pirate is 100G and filefrag reports: 57 extents found
Questions:
- Is this normal?
- I am wondering if the speed of repositioning the disk head to the beginning of a device is fast comparing to any file offset movement. because reading 512B should be elementary ...
Thanks a lot
Last edited by methyl; 07-03-2012 at 07:36 PM..
Reason: please use code tags
Hi ......
I have file system problem when i try to mount get the following message :
mount: /dev/rdsk/c1t4d0s7 not a block device ....
I run fsck it's ok ,,,, after run
newfs -N /dev/dsk/c1t4d0s7 and
fsck -o b=535952 /dev/dsk/c1t4d0s7 .............it's ok ........
At the and when i try... (2 Replies)
Hi,
I am triying to make sure that there exists only one file with the pattern abc* in path /path/. This directory is having many huge files. If there is only one file then I have to take its complete name only to use furter in my script.
I am planning to do like this:
if ; then... (2 Replies)
We are intending to protect a set of user specified files using LVM mirroring where the protected space on which the user files are stored is mirrored on an LV on a different disk. Our problem is that for a user with a custom layout has installed linux with 2 partitons for swap and / and there is... (0 Replies)
I talked with this guy who seems to think loop mounting a fs ext3 image on a directory, as opposed to just using the underlying filesystem, will work better as far as IO conflicts. I have no idea why this would be better? I haven't been able to contact him.
Basically we have a daemon that... (0 Replies)
I use CentOS
I talked with this guy who seems to think loop mounting a fs ext3 image on a directory, as opposed to just using the underlying filesystem, will work better as far as IO conflicts. I have no idea why this would be better? I haven't been able to contact him.
Basically we have a... (1 Reply)
Hello everyone
I am finishing a script allowing me to purge logs on multiple servers, i have one last pb with the ssh command.........it is throwing me the following error :
tcgetattr: Inappropriate ioctl for device (full screen in attached file 1, full script in attached file 2)
It... (15 Replies)
Currently I am using this laborious command
lvdisplay | awk '/LV Path/ {p=$3} /LV Name/ {n=$3} /VG Name/ {v=$3} /Block device/ {d=$3; sub(".*:", "/dev/dm-", d); printf "%s\t%s\t%s\n", p, "/dev/mapper/"v"-"n, d}'
Would like to know if there is any shorter method to get this mapping of... (2 Replies)
Mac Version 10.15.2 (macOS Catalina)
Does anyone know how to change the name of a connected bluetooth device from the command line on macOS?
I am having trouble with various bluetooth devices which I cannot get the "rename" option in the GUI to "save" properly and so I cannot rename a few... (0 Replies)
Discussion started by: Neo
0 Replies
LEARN ABOUT MINIX
vol
VOL(1) General Commands Manual VOL(1)NAME
vol - split input on or combine output from several volumes
SYNOPSIS
vol [-rw1] [-b blocksize] [-m multiple] [size] device
DESCRIPTION
Vol either reads a large input stream from standard input and distributes it over several volumes or combines volumes and sends them to
standard output. The size of the volumes is determined automatically if the device supports this, but may be specified before the argument
naming the device if automated detection is not possible or if only part of the physical volume is used. The direction of the data is
automatically determined by checking whether the input or output of vol is a file or pipe. Use the -r or -w flag if you want to specify
the direction explicitly, in shell scripts for instance.
Vol waits for each new volume to be inserted, typing return makes it continue. If no size is explicitely given then the size of the device
is determined each time before it is read or written, so it is possible to mix floppies of different sizes. If the size cannot be deter-
mined (probably a tape) then the device is assumed to be infinitely big. Vol can be used both for block or character devices. It will
buffer the data and use a block size appropriate for fixed or variable block sized tapes.
Vol reads or writes 8192 bytes to block devices, usually floppies. Character devices are read or written using a multiple of 512 bytes.
This multiple has an upper limit of 32767 bytes (16-bit machine), 64 kb (32-bit), or even 1 Mb (32-bit VM). The last partial write to a
character device is padded with zeros to the block size. If a character device is a tape device that responds to the mtio(4) status call
then the reported tape block size will be used as the smallest unit. If the tape is a variable block length device then it is read or
written like a block device, 8192 bytes at the time, with a minimum unit of one byte.
All sizes may be suffixed by the letters M, k, b or w to multiply the number by mega, kilo, block (512), or word (2). The volume size by
default in kilobytes if there is no suffix.
OPTIONS -rw Explicitly specify reading or writing. Almost mandatory in scripts.
-1 Just one volume, start immediately.
-b blocksize
Specify the device block size.
-m multiple
Specify the maximum read or write size of multiple blocks. The -b and -m options allow one to modify the block size assumptions
that are made above. These assumptions are -b 1 -m 8192 for block devices or variable length tapes, and -b 512 -m 65536 for charac-
ter devices (32 bit machine.) These options will not override the tape block size found out with an mtio(4) call. The multiple may
be larger then the default if vol can allocate the memory required.
EXAMPLES
To back up a tree to floppies as a compressed tarfile:
tar cf - . | compress | vol /dev/fd0
To restore a tree from 720 kb images from possibly bigger floppies:
vol 720 /dev/fd0 | uncompress | tar xfp -
Read or write a device with 1024 byte blocks:
vol -b 1k /dev/rsd15
Read or write a variable block length tape using blocking factor 20 as used by default by many tar(1) commands:
vol -m 20b /dev/rst5
Note that -m was used in the last example. It sets the size to use to read or write, -b sets the basic block size that may be written in
multiples.
SEE ALSO dd(1), tar(1), mt(1), mtio(4).
VOL(1)