Re: aic94xx or libsas crash on X7DB3 supermicro with enclosure and sata drives

[Jeff Garzik <jeff@garzik.org>]

Darrick J. Wong wrote:
> On Mon, Dec 03, 2007 at 05:09:54PM +0100, Krzysztof B??aszkowski wrote:
>> I noticed also another failure when i removed a drive. The event was not 
>> notified by anything (ie the block device and corresponding sg were 
>> registered) so i run dd on this truly "virtual" drive.
>>
>> dd reached D state (as well as scsi_wq) . i think it shouldn't happen no 
>> matter it was AIC failure or LSI expander failure.
> 
> "It's wireless!" ;)
> 
> Seriously, though, it's a good idea to tell the kernel that you're
> about to unplug a disk before actually doing it:
> 
> echo 1 > /sys/block/sdX/device/delete
> 
> This way, the kernel can tell the disk to flush its caches long before
> power actually gets removed.  Otherwise, the device removal code can
> get hung up just like you observed, and whatever's in the write cache
> may or may not actually get written to the media.


What you say is quite true about write cache -- you can clearly lose 
some data by hot-unplugging a device.  And there's nothing we can do 
about that.

But what do you mean by "device removal code can get hung up"?  That 
sounds like a bug we should fix.

	Jeff