ATA -- erratic behaviour when removing disk

Carlos A. M. dos Santos unixmania at
Sat Feb 16 23:08:40 UTC 2008

On Feb 16, 2008 7:07 PM, Jeremy Chadwick <koitsu at> wrote:
> Is anyone aware of the situation where FreeBSD behaves erratically when
> a disk is physically removed without "atacontrol detach ataX" being run
> prior to removal (at least on RELENG_7)?

Yes, I have seen this since 4.5, IIRC.

> Below are my notes from said situation.
> I can provide remote access to this machine (serial-level) to whoever
> wants to hack on it.  I can be available for disk removal/insertion as
> well; just ask.
> Also FWIW: I also tested all this for comparison on Ubuntu Linux earlier
> this morning.  I was able to yank the disk in the middle of an I/O
> operation, resulting in an immediate I/O error from dd.  I took no
> precautions prior to yanking the disk.  Upon reinsertion, the system
> found the disk and I could continue I/O operations on it as if it had
> never been removed.  Only reason I'm pointing this out is that it
> confirms the issue isn't hardware or with vendor implementation, but
> rather specific to the OS.

Congratulations to the Linux folks. Or not, since this looks like a
very risky behavior. Who warrants you that the *same* disk was plugged
back? Blindly continuing to write could easily corrupt the contents of
the second drive.

> --
> | Jeremy Chadwick                                    jdc at |
> | Parodius Networking                  |
> | UNIX Systems Administrator                      Mountain View, CA, USA |
> | Making life hard for others since 1977.                  PGP: 4BD6C0CB |
> Hardware:
>   Supermicro SuperServer 5015M-T+B
>   Intel ICH7
>   AHCI enabled (version 01.10), BIOS-based RAID disabled
>   ad4: 190782MB <WDC WD2000JD-00HBB0 08.02D08> at ata2-master SATA150
>   ad6: 190782MB <WDC WD2000JD-00HBB0 08.02D08> at ata3-master SATA150
> OS installed on /dev/ad4 and OS was booted with verbose logging enabled:
> FreeBSD  7.0-RC2 FreeBSD 7.0-RC2 #0: Fri Feb  8 00:09:57 UTC 2008 root at  i386

[lengthy contents purposefully removed in the reply message]

Carlos A. M. dos Santos

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