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Re: DIOC{G,S}STRATEGY not implemented for all disk devices

--- John Nemeth <> wrote:

> On Jun 19,  3:10pm, Reinoud Zandijk wrote:
> } On Wed, Jan 16, 2008 at 10:21:27PM -0800, John Nemeth wrote:
> } > } There seem to be several almost-identical implementations, in
> } > } sys/dev/dksubr.c, sys/dev/ld.c, and sys/dev/ata/wd.c; an
> implementation
> } > } in sys/dev/scsipi/cd.c that always returns EIO; and
> implementations in
> } > 
> } >      I'm not sure it makes sense for cd.c since that is a
> read-only
> } > device and isn't truely random access.
> } 
> } I have code here for cd.c that actually permits setting the
> strategy; not 
> } used anymore though but for dvd+rw/dvd-ram its a truely random
> access 
> } device allthough it wouldn't be fast.
>      Do these devices work using concentric cylinders similar to the
> way magnetic media works, or do they use the one long spiral track
> the
> way most optical media (and old vinyl records) work?
> }-- End of excerpt from Reinoud Zandijk

Optical disks are...disks. The last time I read up on them, they did
indeed support random access (all have seek times that are far below
tapes). Disk scheduling would probably make a difference even for
read-only media as reordering the requests to optimize seek times
should still apply (mostly for things which do not do such scheduling
internally [most ATAPI, probably most SATA as well]). Not sure what
they mean either...

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