Re: [9fans] ata drive capabilities

[erik quanstrom <quanstro@quanstro.net>]

> Hi 9fans,
> 
> can someone on this list tell me how to interpret the config part of 
> cpu% cat /dev/sdC0/ctl
> inquiry WDC WD1600JB-00REA0                     
> config 427A capabilities 2F00 dma 00550020 dmactl 00550020 rwm 16 rwmctl 0 lba48always off
> 
> I am trying to figure out whether the disk signals the implementation
> of the SMART feature set.
> 
> Kind regards,

in the return of identify (packet) device, if bits 14:16 of word 83 is 1, then
smart support is indicated by word 82 bit 1. otherwise smart isn't supported.

word 49 is the capabilities word and the important bits of the configuration
are:

10,11	iordy configuration
bit 8	dma support
9	lba support

the intel/amd sata driver support smart commands via
	echo smartenable>/dev/sdXX/ctl		# turn drive's smart on.
	echo smart>/dev/sdXX/ctl			# smart report status.
this isn't implemented in the sdata driver, but i think a similar
strategy could be employed.  note: smart commands are not dma
commands.  also, smart support doesn't imply much about what
commands are supported or much about the return values.
report returns if the drive is likely to fail seems the most useful.

bios isn't always helpful in this regard.  some bios don't report
smart status.  some bios do a smart check on power on and won't
boot with a drive that smart considers suspect.  (we have a drive
in the lab that smart declares will fail any minute now.  it's been
this way for 2 years.)  this can be a big problem if you have a
machine with raid that won't boot due to a drive failure.
(why have a raid if one failure means an unbootable machine?)

- erik