Re: Lower HD transfer rate with NCQ enabled?

[Mark Lord]

Phillip Susi wrote:
> Mark Lord wrote:
> > But WD drives, in particular the Raptor series, have a firmware "feature"
> > that disables "drive readahead" whenever NCQ is in use.
>
> Why is this an issue?  Shouldn't the kernel be sending down its own 
> readahead requests to keep the disk busy?

The drive firmware readahead is inherently *way* more effective than
other forms, and without it, sequential read performance really suffers.
Regardless of how software tries to compensate.

This is mostly a problem with the WD Raptor drive, and some other WD drives.
I have not yet encountered/noticed the problem with other brands.

-ml
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