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Special Forums Hardware Filesystems, Disks and Memory SD Card Throughput exceeds - On using "dd" command Post 302294466 by amio on Thursday 5th of March 2009 09:08:25 AM
Old 03-05-2009
SD Card Throughput exceeds - On using "dd" command

Hi All,
Am using dd command to find throughput of my Normal speed SD card.
After mounting the sd card, i run,

Code:
time dd if=/dev/zero of=/mnt/sdcard/Myfile.txt bs=512
count=20480;umount /mnt/sdcard;
20480+0 records in
20480+0 records out
10485760 bytes (10 MB) copied, 0.0658825 s, 159 MB/s

real    0m0.097s
user    0m0.013s
sys     0m0.055s

But the throughput shown(159 MB/s) exceeds the normal speed of SD specification (25MB/sec).

Could you please comment on this??

Thanks,
Amio
 

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VNDCOMPRESS(1)						    BSD General Commands Manual 					    VNDCOMPRESS(1)

NAME
vndcompress, vnduncompress -- compress/uncompress file system images to/from cloop2 format SYNOPSIS
vndcompress [-cd] disk/fs-image compressed-image [blocksize] vnduncompress [-cd] compressed-image disk/fs-image DESCRIPTION
The vndcompress program compresses an existing file system image into a cloop2 compatible compressed file system image. An optional block- size can be given. If omitted, the default of 64kB is used. The vnduncompress command decompress a cloop2-compressed file system image back into a regular image. The file system images that can be handled are not limited to any specific file system, i.e. it is possible to handle images e.g. in ISO 9660 or UFS/FFS format. File system images in the cloop2 format are intended to be used with the vnd(4) driver in compressed mode as configured by the -z option of the vnconfig(8) program, and later mounted with the appropriate -t option to mount(8). OPTIONS
The following options are available: -c Always compress, even if the program was started as vnduncompress. -d Always uncompress (decompress), even if the program was started as vndcompress. EXIT STATUS
The vndcompress and vnduncompress utilities exit with one of the following values: 0 The operation was performed successfully. 1 An error occurred. EXAMPLES
To compress an existing CD-ROM file system image, run the following commands: # vndcompress netbsd.iso netbsd.izo Note that the resulting compressed image cannot be mounted directly via NetBSD's vnd(4) and mount_cd9660(8) commands any longer. Instead, you will have to use the -z option of vnconfig(8). The following example decompresses an existing CD-ROM file system image that was compressed in the cloop2 format into a regular file that can then be mounted: # vnconfig vnd0 KNOPPIX.iso # mount -t cd9660 -o ro /dev/vnd0d /mnt # vnduncompress /mnt/KNOPPIX/KNOPPIX /var/tmp/knoppix.iso # umount /mnt # vnconfig -u vnd0 # # vnconfig vnd1 /var/tmp/knoppix.iso # mount -t cd9660 -o ro /dev/vnd1d /mnt # ls /mnt .rr_moved cdrom floppy lib opt sbin usr bin dev home mnt proc sys var boot etc initrd none root tmp vmlinuz # umount /mnt # vnconfig -u vnd1 As an alternative, if your vnd(4) was compiled with VND_COMPRESSION, you can use vnconfig(8) to access the cloop-compressed image directly, e.g., # vnconfig vnd0 KNOPPIX.iso # mount -t cd9660 -o ro /dev/vnd0d /mnt # vnconfig -z vnd1 /mnt/KNOPPIX/KNOPPIX # mount -t cd9660 -o ro /dev/vnd1d /mnt2 # ls /mnt2 .rr_moved cdrom floppy lib opt sbin usr bin dev home mnt proc sys var boot etc initrd none root tmp vmlinuz # df /mnt /mnt2 Filesystem Size Used Avail Capacity Mounted on /dev/vnd0a 692M 692M 0B 100% /mnt /dev/vnd1a 1.9G 1.9G 0B 100% /mnt2 # umount /mnt2 # vnconfig -u vnd1 # umount /mnt # vnconfig -u vnd0 Note how the 1.9GB big filesystem on /mnt2 is mounted from the compressed file stored on the 692MB CD mounted on /mnt. To create a com- pressed file system image of an existing directory and mount it, run: # makefs -t ffs include.fs /usr/include # vndcompress include.fs include.fs.cloop2 # vnconfig -z vnd0 include.fs.cloop2 # mount -o ro /dev/vnd0a /mnt # ls /mnt To undo the steps, run: # umount /mnt # vnconfig -u vnd0 # rm /tmp/include.fs.cloop2 # rm /tmp/include.fs SEE ALSO
gzip(1), vnd(4), mount(8), mount_cd9660(8), vnconfig(8) AUTHORS
The vndcompress utility was written by Florian Stoehr <netbsd@wolfnode.de>. The vndcompress manual page was written by Florian Stoehr <netbsd@wolfnode.de> and Hubert Feyrer <hubertf@NetBSD.org>. BSD
December 12, 2005 BSD
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