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Date:      Wed, 31 Mar 1999 17:03:18 +1000
From:      Bruce Evans <bde@zeta.org.au>
To:        freebsd-current@FreeBSD.ORG, jobaldwi@vt.edu, sos@freebsd.dk
Cc:        sobomax@altavista.net
Subject:   Re: UPDATE4: ATA/ATAPI driver new version available.
Message-ID:  <199903310703.RAA00353@godzilla.zeta.org.au>

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>I had similar problems in -stable with the old ATA drivers.  I was having weird
>swap errors, so I booted w/o swap and dd'd my swap partitions to check for read
>or write errors.  I could do a dd if=/dev/wd0s3b of=/dev/null fine.  But, when
>I tried a write from /dev/zero (dd if=/dev/zero of=/dev/wd0s3b) it locked up. 

Writing beyond EOF to a buffered disk device hangs both 3.x and -current.
The failing writes are retried forever.

>> dd if=/dev/zero of=/dev/wd0s3b bs=64k
>
>Disk activity for a while (i think it actually goes long enough to finish the
>write), and then the machine locks up.  

The easiest fix is: don't do that.  Unbuffered disk devices are slower
than buffered ones.  Buffered disk devices are only useful for:
- mounting on
- finding bugs in the buffer cache.

Bruce


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