Subject: Re: wedges and DEV_BSIZE (Was Re: removing VOPs)
To: Pavel Cahyna <email@example.com>
From: Reinoud Zandijk <firstname.lastname@example.org>
Date: 10/11/2005 13:56:06
Content-Type: text/plain; charset=us-ascii
On Tue, Oct 11, 2005 at 10:39:16AM +0200, Pavel Cahyna wrote:
> Wouldn't it make sense if other drivers having larger sectors did the
> same? Why can't DVD/CD+-(M)R(W) do read-modify-write?
technically they can, though the penalties are huge.
1) switching from reading to writing and back take typically
takes significant time in the order of about *half a second* on a
2) you will loose sectors when writing on recordables. This results in a
few logical sectors NOT being adressable anymore. I dont have to tell
you what an administrative mess this gives on allocation.
3) CD-MRW and DVD+(M)RW are the only ones that allow you to write a *single
sector*. Others even require a whole ECC block to be written forcing a
read/modify/write cycle itself if not in cache so the filingsystem
implementation needs to be optimised to minimise this as much as
possible or performance will be very bad.
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