[Bug 172287] Re: hdparm's feedback about -B values is misleading

[Bob Harvey]

I don't think this is invalid at all.
I agree, following reading round, that the man page is incorrect.

Looks to me like the original report was never read or acted upon.

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https://bugs.launchpad.net/bugs/172287

Title:
  hdparm's feedback about -B values is misleading

Status in “hdparm” package in Ubuntu:
  Invalid

Bug description:
  Binary package hint: hdparm

  hdparm says 255 disables power management on an harddrive but using
  255 is undefined and doesn't disable power management on the harddrive
  for everyone. hdparm doesn't mention that using 128 will reduce power
  use as much as possible but not permit spin-down unless you set the
  spin down value using hdparm -S.

  tferero received an email from Bruce Allen. From :
  http://www.linuxquestions.org/questions/showthread.php?p=2945630#post2945630

  [quote=Bruce Allen]
  Hi T-,

  I just learned about this buzz from a colleague yesterday.

  I don't have any experience with your Samsung drive. I suggest that you
  run a sort self-test '-t short' and wait until it completes. The drive
  age should then be shown in the self test log. Then experiment with the
  different -v and -F options to see how the drive is storing its lifetime.

  IMPORTANT INFORMATION BELOW: PLEASE PASS BACK TO THE UBUNTU COMMUNITY

  I think that the -B value of 255 is incorrect. You should use 254 for
  maximum performance. 255 IS DOCUMENTED AS 'RESERVED' IN THE ATA/SATA
  SPECS. THE BEHAVIOR OF -B 255 THUS IS NOT PREDICTABLE AND IT MAY HAVE NO
  EFFECT. Also according to the ATA/SATA specs any value greater than or
  equal to 128 will 'not permit the device to spin down to save power'. So
  128 will reduce power use as much as possible but not permit spin-down.

  References:
  http://www.t13.org/Documents/UploadedDocuments/docs2007/D1532v1r4b-AT_Attachment_with_Packet_Interface_-_7_Volume_1.pdf
  PDF page 273 Document page 253
  Table 43 (and the paragraph immediately following it).

  So I suggest you try some different -B values such as -B 254 or -B
  128.

  The hdparm man page says 'values of 255 will disable Advanced Power
  Management'. I think this is a mistake in the man page. According to the
  ATA/SATA specs referenced above, the value 255 is reserved and has vendor
  dependent meaning (or has no effect).

  Cheers,
  Bruce
  [/quote]

  Bruce Allen is :
  * author of "Monitoring Hard Disks with SMART", Linux Journal, 2004) :
  http://www.linuxjournal.com/article/6983
  * maintainer of the website http://smartmontools.sourceforge.net/

  blackhole54 notified us here about this here :
  http://ubuntuforums.org/showpost.php?p=3690862&postcount=15

  hdparm is currently misleading both in the manpage and on the
  commandline :

  using hdparm on the commandline :
  =================================
  $ sudo hdparm -B 254 /dev/sda

  /dev/sda:
   setting Advanced Power Management level to 0xfe (254)

  $ sudo hdparm -B 255 /dev/sda

  /dev/sda:
   setting Advanced Power Management level to disabled
  roald at T-2500:~$ sudo hdparm -B 254 /dev/sda
  ===================================

  from hdparm's manpage :

  ===========================================
         -B     Set Advanced Power Management feature, if the drive supports it.
                A low value means aggressive power management and a  high  value
                means better performance. A value of 255 will disable apm on the
                drive.
  ==========================================

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