Re: Can't disable NCQ, /sys/block/sdc/device/queue_depth is readonly
There are two reasons:
1) After coming across a simple random seek benchmark, I am finding that my
WD raptor 10K drive is giving me about 10 ms seek time, where other raptors
benchmarked with the same program are reporting 7.5 - 8.0 ms. This is
a fairly substantial difference, and I am trying to track it down. (As
an aside, I found that
enabling acoustic management made a great difference on several drives
- about a 30% increase is seek time.)
2) From my reading about NCQ, one of the quirks of Raptors is that
when NCQ is enabled, the drive disables its internal readahead. This
results in significantly reduced sequential throughput. Apparently
the windows drivers have some workarounds to deal with this.
I'l like to be able to test to see what effect NCQ has on these
issues. I find it very strange that the official interface for
controlling this seems to be broken (or misconfigured on my system),
and I could not find anything useful about this
via google. (I did find a couple other posts about the same problem,
but no resolution.)
On 5/5/07, Greg Folkert <greg@gregfolkert.net> wrote:
On Fri, 2007-05-04 at 19:13 -0700, Roy Franz wrote:
> I can't disable NCQ due to the sysfs file being read-only:
>
> amd64:/sys/block/sdc/device# ls -al queue_depth
> -r--r--r-- 1 root root 0 2007-05-04 18:44 queue_depth
> amd64:/sys/block/sdc/device#
> amd64:/sys/block/sdc/device# echo 1 > queue_depth
> bash: queue_depth: Permission denied
> amd64:/sys/block/sdc/device#
>
> I am running amd64 Etch, with this machine running a 2.6.20 kernel. I checked
> another AMD64 machine that is running the stock Debian 2.6.18-4 kernel
> and the file is also readonly there.
>
> This seems to be the officially supported way of enabling/disabling NCQ.
>
> Has anybody else run into this or have a solution?
Why would you want to disable NCQ? You are using libSATA right?
Is your controller in the blacklist? or Are you specifically having some
kind of issue?
--
greg, greg@gregfolkert.net
Novell's Directory Services is a competitive product to Microsoft's
Active Directory in much the same way that the Saturn V is a competitive
product to those dinky little model rockets that kids light off down at
the playfield. -- Thane Walkup
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