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Date: Wed, 19 Feb 1997 16:52:38 -0800 (PST)
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To: joerg_wunsch@uriah.heep.sax.de
CC: james@wgold.demon.co.uk, hackers@FreeBSD.org, dufault@hda.com
In-reply-to: <Mutt.19970219223544.j@uriah.heep.sax.de>
Subject: Re: [Fwd: Failed mail: unknown user]
From: asami@vader.cs.berkeley.edu (Satoshi Asami)
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 * >  - if the OS tells me it has a successful write through the
 * >    disk device, can I rely on:
 * > 
 * >    a) the data is on the platter
 * 
 * It is.  Since physio(9) waits for the completion, you should be
 * notified of any lower-level errors.  Note that this is _unlike_ with
 * the block devices, where writing happens asynchronously, so the kernel
 * did already declare the write operation as successful by the time it
 * notices an error.

Really?  I think drives have their own cache, and if they have write
buffering turned on, they will happily return "write complete" when
they are only holding data in the buffer.

I know Seagate ST15150WC (old Barracuda 4) had the write buffer
disabled, while Quantum 34300WC (Atlas 4) had it enabled.  If you
really want to make sure you write through to the platter, either get
one of those that don't have it turned on or turn it off by youself
(I heard it's in one of the SCSI mode pages).

Satoshi