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Special Forums Hardware DD command using block device as input Post 302666027 by Corona688 on Tuesday 3rd of July 2012 02:23:42 PM
Old 07-03-2012
Quote:
Originally Posted by nytty
Why is read-ahead a problem since above is only a 512bytes read
Because, I repeat, you are not getting raw access here.

You are not getting raw access.

You are not telling the drive 'move to sector x, read'.

You are telling the operating system 'give me data from position x'.

The operating system goes 'Hmmm, someone asked for that a little while ago', pulls it from cache, and gives it to you without touching the disk.

Dropping caches all the time is a bad idea. If you really want to get disk access speeds, use hdparm.

Quote:
Then if the cache is the reason, it should affect the file as well, but I am getting the same result for all reps?
Your results aren't accurate. You're running huge programs to do tiny things and most of what you're measuring is going to be error and bias of some sort. If you want to do real benchmarks, hdparm.

There isn't a significant difference between file and raw disk unless your file is very badly fragmented.
 

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tgt-setup-lun(8)					      System Manager's Manual						  tgt-setup-lun(8)

NAME
tgt-setup-lun - creates a target, adds a device to the target and defines initiators that can connect to the target SYNOPSIS
tgt-setup-lun -d device -n target_name [initiator_IP1 initiator_IP2 ...] [-h] DESCRIPTION
Starts tgtd if necessary and creates a target according to the supplied target_name. The format of the target name is as follows: iqn.2001-04.com.<hostname>-<target_name> The target name must be unique. The script then adds the requested device to the target. If specific IP addresses are defined, it adds them to the list of allowed initia- tors for that target. If no IP addresses is defined, it defines that the target accepts any initiator. EXAMPLES
Create a target that uses /dev/sdb1 and allows connections only from 192.168.10.81: tgt-setup-lun -d /dev/sdb1 -n my_target 192.168.10.81 Create a target that uses /dev/sdb1 and allows connections only from 192.168.10.81 and 192.168.10.82: tgt-setup-lun -d /dev/sdb1 -n my_target 192.168.10.81 192.168.10.82 Create a target that uses /dev/sdb1 and allows connections from any initiator: tgt-setup-lun -d /dev/sdb1 -n my_target Display help: tgt-setup-lun -h AUTHOR
Written by Erez Zilber REPORTING BUGS
Report bugs to <stgt@vger.kernel.org> COPYRIGHT
Copyright (C) Voltaire Ltd. 2008. tgt-setup-lun(8)
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