On Tue, Apr 02, 2002 at 03:42:43PM -0800, James A. Peltier wrote:
> so when I issue the commands
>
> atactl /dev/wd0c readaheadenable
> atactl /dev/wd0c writecacheenable
>
> these features should now be turned on.
Probably, although strictly speaking you only _instructed_ the disk to
enable these functions. It did not return an errormessage, so the disk
did not complain, but there are drives out there that silently ignore
certain commands. Usually this means that the command in question is
irrelevant.

> does it show up in identify if turned off ???
"atactl /dev/wd0c identify" reports capabilities and command sets (such as
enabling/disabling readahead, caching, SMART) under the headings "Device
capabilities" and "Device supports the following command sets"
respectively. This indicates the _support_ for these commands by the
harddisk, not their status. In essence, a set of bitfields in the device
are read that indicate whether the host can expect certain sets of
commands to succeed, such as enabling SMART.
Some of these capabilities can be selectively enabled/disabled, these
show up under the heading "Device has enabled the following command
sets/features". On modern drives, "read look-ahead" and "write cache"
indicate that readaheadenable and writecacheenable succeeded. Older
drives may ignore these commands and/or fail to report their status.
In general most drives internally already use read look-ahead, so
enabling read look-ahead will usually not increase performance.

Note that you need to repeat these commands each time the device is
reset, i.e. after a reboot. Putting the atactl-commands in /etc/rc.local
is a good idea.

With kind regards,
Wouter

--
Wouter Slegers
Your Creative Solutions
"Security solutions you can trust and verify."
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