Re: Questions about SATA hotplug in linux 2.6

[Tejun Heo <htejun@gmail.com>]

Jeff Garzik wrote:
> Shane Huang wrote:
>> 1. If users unplug one SATA HDD(no-root partition) or SATA ODD when
>> the system is running, then plug it back to the same SATA port,
>> Should the system and SATA HDD/ODD still work well?
> 
> Yes.

To add a bit, libata hotplug has grace time of at least 15secs.  If the
same device is plugged out and then plugged in in that time, libata
considers that the device and/or connection has suffered transient
failure and assumes it's the same device and there's no modification to
its content.

This means that if you disconnect a harddrive, write to it and then
connect it back in the grace period corruption will occur.  It will be
fun to have some sort of competition to actually do this.  :-)

>> These questions come up when our QA test our SB700 SATA drivers,
>> but I don't know the SATA hotplug support in linux 2.6.
>> Is there any guy who can give some official confirmation? :-)
> 
> The main thing of note with regards to hotplug is that the associated
> device (/dev/sdb, /dev/scd0, etc.) may change between plug and unplug.
> For example, if you unplug a SATA HDD then plug it back in, the user
> might see /dev/sdb disappear, and /dev/sdd appear -- even if it is the
> exact same HDD, on the exact same port.

Yeah, using LABEL and/or UUID is a good idea.  In the future, it will be
nice to have persistent block device name as netdevices do.

-- 
tejun