[smartmontools-support] problem with scterc on a mac

[Dennis Couzin]

Dear Christian,
Your quote from the 2008 ATA8-ACS final draft:	
	"Read and Write Command Timer values are set to default values at 
	power-on but may be altered by an SCT command at any time. A device 
	shall not change these settings while processing a hardware reset or a 
	software reset."
The phrase "these settings" in the second sentence is ambiguous: it can refer either to the default values mentioned in the first sentence or to the altered values mentioned later in the first sentence.  To a normal, untechnical English reader, "these settings" would refer to the altered values.  On that reading, if a "power-on" entails a "reset", the second sentence contradicts the first.  But if a "power-on" does not entail a "reset", there will be no contradiction.  

Thus the 2008 ATA8-ACS language was sloppy, and WD, whose man edited the specification, read it one way, while Toshiba read it another way.  Now we have the humorous situation where users are discovering their ERC settings to be "persistent" for some drives and "non-persistent" for other drives.  (For example, TAC's 23 July 2019 post at https://www.ixsystems.com/community/threads/checking-for-tler-erc-etc-support-on-a-drive.27126/page-9 happily announced that his Toshiba N300 retained its ERC values after reboot.)

Ca. 2008, WD supplied a DOS program wdler.exe to make ERC settings on its hard drives.  Could its settings have been anything but "persistent"?  

Sincerely,
Dennis

-----Original Message-----
From: Smartmontools-support <smartmontools-support-bounces at listi.jpberlin.de> On Behalf Of Christian Franke
Sent: Saturday, 8 February 2020 17:35
To: Dennis Couzin <dcouzin at yahoo.com>
Cc: Smartmontools-support at listi.jpberlin.de
Subject: Re: [smartmontools-support] problem with scterc on a mac

Dennis Couzin wrote:
> Dear Christian,
> I don't understand why you asked, but I confirmed that  "smartctl -l scttemp" running on Darwin does print the temperature table:
>
> 	evas-system:~ evaheldmann$ smartctl -l scttemp /dev/disk4
> 	smartctl 7.0 2018-12-30 r4883 [Darwin 16.7.0 x86_64] (local build)
> ...
> 	Current Temperature:                    28 Celsius
> 	...
> 	  13    2020-02-08 13:47    28  *********

I asked because -l scttemp uses the same command (SMART_WRITE_LOG) as -l 
scterc (get), but with different parameters.


> I also don't understand the 2008 ATA8-ACS final draft's statement: "a device shall not change these settings while processing a hardware reset or a software reset".  What are hardware or software resets and when do they occur?

These are device resets issued via specific (hardware) signal sequences 
on the SATA link or specific SATA (software) commands. Those resets 
typically occur during boot and may occur later if the device driver 
detects problems, e.g. SATA CRC errors.


> Powering off and on certainly does change the ERC settings on some drives (e.g., my WD Red Pro, manufactured 2016) but not on other drives (e.g., my Toshiba N300, manufactured 2019).

Then the WD Red Pro honors the ATA standard but the Toshiba N300 does 
not. A power cycle shall reset the ERC settings to factory defaults.

Regards,
Christian

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