I understand async is always unsafe. I don't mean async. I don't use async.
I mean the hardware write cache built into the ATA drives. I read somewhere
that, unlike SCSI drives, the write cache in ATA drives results in
misinformation about when data was actually written to disk. So, as I
understand it, you can't use soft updates with the drive's write cache on.
So you have to chose between the drive's write cache or using soft updates.
The write cache I'm talking about is the one that appears below, and can be
disabled with the atactl wd0 writecachedisable.
# atactl wd0 identify
Model: ST380011A, Rev: 8.11, Serial #: 5JVJL5MG
Device type: ATA, fixed
Cylinders: 16383, heads: 16, sec/track: 63, total sectors: 156301488
Device capabilities:
ATA standby timer values
IORDY operation
IORDY disabling
Device supports the following standards:
ATA-1 ATA-2 ATA-3 ATA-4 ATA-5 ATA-6
Device supports the following command sets:
READ BUFFER command
WRITE BUFFER command
Read look-ahead
Write cache
Power Management feature set
SMART feature set
Flush Cache command
Device Configuration Overlay feature set
DOWNLOAD MICROCODE command
SMART self-test
SMART error logging
Device has enabled the following command sets/features:
READ BUFFER command
WRITE BUFFER command
Read look-ahead
Write cache
Power Management feature set
SMART feature set
Flush Cache command
Device Configuration Overlay feature set
DOWNLOAD MICROCODE command
-----Original Message-----
From: Theo de Raadt [mailto:[EMAIL PROTECTED]
Sent: Friday, September 30, 2005 11:51 AM
To: Michael Favinsky
Cc: '[email protected]'
Subject: Re: ATA Soft Updates or Write Caching
> When using ATA drives, I have to make a choice between write caching
> or soft updates, since write caching with soft updates creates an unsafe
situation.
I assume by 'write caching' you mean async.
No. You have that wrong.
async is always unsafe.
Everything else you say says that you consider performance more important
than safety. There is no balance. We could remove the options that provide
rope, but then the amount of whiners would increase..
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