Transfer Rate Disk Post: 302505635

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Top Forums UNIX for Dummies Questions & Answers Transfer Rate Disk Post 302505635 by Corona688 on Thursday 17th of March 2011 01:16:04 PM

03-17-2011

Registered User

dd is a general purpose data moving command. It's sometimes used for moving data from one raw disk to another but it's a flexible command and doesn't care what kind of files or devices it's talking to.

dd by itself just reads stdin and writes back to stdout, so dd < filename > newfile is effectively the same thing as cp.

It does it in blocks of 512 bytes by default, which is a bit inefficient, so dd bs=1048576 < filename > newfile may be much faster. Beyond a certain point making the buffer bigger doesn't help.

So all I'm doing is having dd read from one file and write to another, and while it's running, sending it the signal SIGUSR1 which casues it to print statistics. Or you could wait for it to end, or kill it with ctrl-C, and it'll print statistics as it ends.

cache effects are when the OS doesn't immediately store what you've written to file on disk, just in memory. This is great for programs since they don't have to wait for the disk to catch up but troublesome for benchmarks. dd in linux supports the oflag=sync option to tell it not to do that.

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LEARN ABOUT HPUX

format

format(1M)																format(1M)

NAME

       format - format an HP SCSI disk array LUN

SYNOPSIS

       device_file

DESCRIPTION

       formats	one  LUN of the HP SCSI disk array associated with device file, device_file.  The format will usually be a soft or zeroing format,
       in which the controller writes zeroes to the data area and parity area, if any, of the LUN.

       NOTE: The above should always be true of a sub-LUN, but the controller might decide, based on certain conditions, to do a full format of  a
	      regular  LUN,  which consists of sending a mode select and a media initialization command to the physical drive(s) in question, fol-
	      lowed by zeroing the data and parity area, if any.  The conditions which will cause a full format to be done are as follows:

	      1.     The controller received a Mode Select command which requires a drive sector size change.

	      2.     The controller received a Mode Select command which changed a parameter in the Format Device Page(0x03).

	      3.     The LUN contains one or more failed drives.  In this case only a certain subset of the drives containing  the  failed  drives
		     will be formatted.

	      4.     Either the FmtData or the CmpLst bit in the Format Unit CDB is set.

RETURN VALUE

       returns the following values:

	     0	   Successful completion.
	    -1	   Command failed.

DIAGNOSTICS AND ERRORS

       Errors can originate from problems with:

	      o

	      o  SCSI (device level) communications

	      o  system calls

   Error messages generated by format:
       An error in command syntax has occurred.
	      Enter command again with all required arguments, in the order shown.

       To ensure that
	      does  not  modify a disk array that is being used by another process, attempts to obtain exclusive access to the disk array.  If the
	      disk array is already opened by another process (for example, LVM -- the Logical Volume Manager), a "" error message is returned	by
	      the  driver.   To  eliminate  the  "" condition, determine what process has the device open.  In the case of LVM, it is necessary to
	      deactivate the volume group containing the array before formatting array LUNs (see vgchange(1M)).

       The LUN number, which is derived from the device file name, is out of range.

       The addressed LUN
	      is not configured, and thus is not known to the array controller.

       Utilities must be able to open the device file for raw access.

       The device being addressed is not an HP SCSI disk array.

   SCSI (device level) communication errors:
       Sense data associated with the failed operation is printed.

   Error messages generated by system calls:
       uses the following system calls:

	      and

       Documentation for these HP-UX system calls contains information about the specific error conditions associated with each  call.	 does  not
       alter the value of The interpretation of for printing purposes is performed by the system utility

EXAMPLES

       To format the HP SCSI disk array LUN on a Series 800:

WARNING

       The command will destroy all user data on the addressed LUN.

DEPENDENCIES

       The HP C2425 and HP C2427 disk arrays are only supported on Series 700 systems running HP-UX version 9.0X.

       The HP C2430 disk array is supported on Series 700 and 800 systems running HP-UX versions 9.0X and 10.0X.

AUTHOR

       was developed by HP.

																	format(1M)