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Top Forums Programming write() issue during a low level hdd access Post 302397636 by Corona688 on Monday 22nd of February 2010 09:09:20 PM
Old 02-22-2010
Quote:
Originally Posted by sponnusa
Also, according to the ata specifications, timeout would be only for certain operations and ranges in the order of nanaseconds (400ns is default i believe).
And might not work in this case as it has to pass through the kernel / driver layers.
I think you're looking at the over-the-cable protocol, not how data is communicated. It's not synchronous -- after all, one seek alone might take considerably longer than 400 nanoseconds. So the computer can tell the drive "do a big DMA transfer and send an interrupt once the data's actually in memory." and the drive will answer in 400 nanoseconds, "OK I will do a big DMA transfer". But the transfer itself can take an unspecified amount of time.
Quote:
In one of the earlier posts, you pointed out about the option of having a driver for talking to the drives. Is there any generic direction / pointers you can point to or I should start at libata / scsi drivers?
I was not being facetous when I suggested the linux kernel mailing list. They'd know far better than we would about low-level I/O.

Yes, hdparm only works for SATA and IDE. You want raw I/O, so you'll have to speak the drive's language.

Last edited by Corona688; 02-22-2010 at 10:28 PM..
 

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hdparm.conf(5)						     hdparm configuration file						    hdparm.conf(5)

NAME
hdparm.conf - Debian configuration file for hdparm DESCRIPTION
This is the default configuration for hdparm for Debian. It is a rather simple script, so please follow the following guidelines :) Any line that begins with a comment is ignored - add as many as you like. Note that an in-line comment is not supported. If a line consists of whitespace only (tabs, spaces, carriage return), it will be ignored, so you can space control fields as you like. ANYTHING ELSE IS PARSED!! This means that lines with stray characters or lines that use non # comment characters will be interpreted by the initscript. This has probably minor, but potentially serious, side effects for your hard drives, so please follow the guidelines. Patches to improve flexibilty welcome. Please read /usr/share/doc/hdparm/README.Debian for notes about known issues, especially if you have an MD array. Note that if the init script causes boot problems, you can pass 'nohdparm' on the kernel command line, and the script will not be run. Setting an option outside of one of the stanzas enables it for all drives. If an option is listed twice, the second instance replaces the first. /sbin/hdparm is not run unless a block of the form: DEV { option option } exists. This blocks will cause /sbin/hdparm OPTIONS DEV to be run. Where OPTIONS is the concatenation of all options previously defined outside of a block and all options defined with in the block. OPTIONS
-q be quiet quiet -a sector count for filesystem read-ahead read_ahead_sect = 12 -A disable/enable the IDE drive's read-lookahead feature lookahead = on -b bus state bus = on -B apm setting apm = 255 -B apm setting when on battery apm_battery = 128 -c enable (E)IDE 32-bit I/O support - can be any of 0,1,3 io32_support = 1 -d disable/enable the "using_dma" flag for this drive dma = off -D enable/disable the on-drive defect management defect_mana = off -E cdrom speed cd_speed = 16 -k disable/enable the "keep_settings_over_reset" flag for this drive keep_settings_over_reset = off -K disable/enable the drive's "keep_features_over_reset" flag keep_features_over_reset = on -m sector count for multiple sector I/O mult_sect_io = 32 -P maximum sector count for the drive's internal prefetch mechanism prefetch_sect = 12 -r read-only flag for device read_only = off -s Enable/disable the power-on in standby feature poweron_standby = off -S standby (spindown) timeout for the drive spindown_time = 24 -u interrupt-unmask flag for the drive interrupt_unmask = on -W Disable/enable the IDE drive's write-caching feature write_cache = off -X IDE transfer mode for newer (E)IDE/ATA2 drives transfer_mode = 34 -y force to immediately enter the standby mode standby -Y force to immediately enter the sleep mode sleep -Z Disable the power-saving function of certain Seagate drives disable_seagate -M Set the acoustic management properties of a drive acoustic_management -p Set the chipset PIO mode chipset_pio_mode --security-freeze Freeze the drive's security status security_freeze --security-unlock Unlock the drive's security security_unlock = PWD --security-set-pass Set security password security_pass = password --security-disable Disable drive locking security_disable --user-master Specifies which password to select security_mode = u --security-mode Set the security mode security_mode = h Root file systems. Please see README.Debian for details. ROOTFS = /dev/hda Blocks beginning with the keyword 'command_line' instead of a device identifier are no longer supported for backwards compatibility by this version of hdparm. Options must be introduced by a correct device identifier instead so that they will be applied when the device becomes available. AUTHOR
hdparm was written by Mark Lord <mlord@pobox.com> The init script and configuration file are currently maintained by Stephen Gran <sgran@debian.org>, but are the result of the work of many people. This manual page was created by Stephen Gran <sgran@debian.org> for the Debian GNU/Linux system (but may be used by others). Stephen Gran August 10, 2005 hdparm.conf(5)
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